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An 8-bit single-chip microcomputer for automotive engine control
An 8- bit single- chip microcomputer for automotive engine control For microelectronics to be widely applied to the motor industry, computers must be inexpensive and easy to operate as well as being reliable, robust and multifunctioned. S Katori, J Iwasaki and Y Maehashi describe a single-chip microcomputer which has been designed with these requirements in mind An 8-bit single-chip microcomputer tJPD7811 for automotive engine control has been developed. This microcomputer has been improved both in its peripheral functions and its instruction set over existing single-chip microcomputers. It allows the conversion o f the engine control system, which is composed of a number of LSI chips, to a singlechip configuration. It is now therefore possible to develop a compact reliable low cost engine control system. In this paper, the design target, the reinforced peripheral functions and the instruction set o f the microcomputer are presented.
microprocessors automotive enginecontrol The rapid growth of LSI technology keeps its pace year after year and so the microcomputer has attained higher functionality yet lower cost because of the continuous improvements in chip integration. The current microcomputers can be categorized into the two: one for the general-purpose applications and the other for single-chip microcomputers. In line with the continued improvement in performance, some general-purpose microprocessors have already exceeded the functionality of minicomputers. At the same time, the larger onchip memory, faster CPU and onchip peripherals of single-chip microcomputers are no longer a illusion, thanks to increased integration. It allows the single-chip microcomputer to act as a higher-performance controller. In line with this trend the single-chip microcomputer, /aPD7811, has been developed for automotive engine control. In general, a microcomputer for total engine control system requires the following functions: • high quality A/D converter • pulse-output handling capability such as flexible pulseposition and pulse-width modulation • high speed data processing capability and sophisticated peripheral control for program efficiency Present technology has made it possible to integrate all these necessary functional blocks required for total engine control as well as high-level bit processing, large memory capability and other essential functions onto a single chip. Plant, 1753 5himonumabe, Nakahaka-ku, Kawasaki 211, Japan This paper is based on a presentation given at ISATA 81, the
Nippon Electric Company Ltd, Tamagawa
International Symposium on Automotive technology and Automation, in Stockholm, Sweden. The proceedings of ISATA 81 are available from Automotive Automation Ltd, Croydon, UK
v o / 6 n o 7september 1982
SYSTEM FEATURES The microcomputer was designed to have more onchip peripherals and an instruction set which is better suited to engine control applications.
Peripheral functions In microcomputer-based engine control optimized air:fuel ratio and spark timing are calculated from various engine parameters and environmental parameters such as air-flow and engine speed. Fuel injectors and ignitors are controlled with series of pulse signals whose output timing and width are based on the above calculations. However, in general, engine control systems have the two problems. Firstly. since almost all parameters, such as air-flow and air-temperature which are derived from analogue sensors, needed for engine control must be converted to digital data. Secondly, an accurate pulse-output capability is necessary since pulse generation must be precisely controlled, based on the calculation results of pulse-output timing and pulse width. In order to control the pulse position and the pulse width precisely, the pulse output capability must be free from software output control. To solve these problems, the pPD7811 has been equipped with an 8-bit converter, 16-bit timer]event counter and a pair of 8-bit interval timers. The onchip A/D converter has eight analogue inputs so most of the analogue signals from various sensors can be handled without additional A/D LSI chips. The 16-bit timer/event counter is designed for flexible pulse-position and pulse-width modulation. By using this 16-bit timer/ event counter, pulses for the actuator control can be easily and precisely generated. On the other hand, existing engine control systems use many dedicated LSI chips, for A/D conversion and pulseoutput control. In such systems, which comprise several LSI chips, a different problem arises, because each LSI chips must be linked by a parallel databus. Multichip systems in a strong noise environment, such as an engine room, may be in danger of misoperation because various noises are induced on the databus of the control system. Thus such engine control systems essentially contain problems of both reliability and security. Since the IaPD7811 makes a direct interface between the CPU and the various analogue sensors and actuators, the engine control system itself is free from noise transmitted over the databus. This results in improvement of the
0141-9331[82[070347--07 $03.00 © 1982 Butterworth & Co (Publishers) Ltd
347
reliability and the security of the engine control system. In addition to these facilities, the microcomputer also contains a serial communication interface in order to match a distributed control system which will come into use in near future. Increasing the control items of an automative management system to include not only dashboard and engine control but also transmission and suspension makes a distributed system even more vital. The importance el serial data transfer is thus increased.
executed within 8 #s, or a divide operation ol 16 x S-bii in 14/Js. The bit manipulation instructions of bit setting, resetting or testing are improved. Thus and I/O line can be selectively read, set or reset with a single instruction ~vithout having to retain an IjO pin image in software and various flags to hold the controlled status can be readily set up in memory.
ARCHITECTURE Due to the NMOS process, the/IPD781 I contains the functional blocks such as 4k of ROM, 256 byte of RAM, 44 I/O lines, an 8-bit A/D converter, 16-bit timer/event counter, two 8-bit interval timers and serial communication interface on the single chip as shown in Figure 1. Further, the 8-bit single-chip microcomputer has 16-bit operation instructions, including those for multiply and divide table look-up instructions and bit-manipulation instructions. In addition to the stand-alone system configuration, tile bus-compatibility of the ~PD7811 with 8085A enables building up of a large-scale control system with memories and other LSI chips.
I n s t r u c t i o n set In the control system, since the air:fuel ratio and spark timing should be controlled in real time, the CPU has to calculate the pulse-output timing and pulse width for the injector and ignitor at a high speed. The output timing and width of pulses can generally be got by looking up in the two-dimensional table which gives two different types of data. This data is converted from analogue to digital, and by two-dimensional interpolation and other calibrations. Accordingly, to implement the high-speed processing, the instruction cycle must not only be shortened, but there must an instruction set provided that is more suitable for data processing in the above, such as in interpolation, etc. The instruction cycle time of the/JPD7811 is 1 #s. It has not only a short processing time, but also contains an powerful instruction set with such functions as 16-bit data transfer, 16-bit arithmetic and logical operations and table look-up or multiply/divide in order to handle data more efficiently. The multiply operation of 8 x 8-bit can be
Memory
and addressing
The single-chip microcomputer has a total of 64k of memory space in which the 4k internal ROM, 256 byte internal RAM and 60k external expandibl¢ memory are assigned (Figure 2). Accordingly, a space of 60k out of the 64k memory space, except the internal ROM area, can be used either for program memory or data memory. XI
N., INTI
X2
VDD
Address bus Interrupt
INT2/TI INC/DEC SP
Serial I/0
B
I
TI/PG s o - ~
8-bit interval
V
timer O, I
EA
TOIPC 4
I
ClIPC5 ~ COO/PC ~
6COl I PC 7
I
AVcc ~ VASS
L E C A
H D
H'
L'
D' B' V'
E' C' A'
(,256 byte)
EA'
..q
event counter
converter
ANo 7
",6 instantaneous I register _ J
CRR2 CRR3
Instantaneous
I
I
II PFo_7
S PDo_7
.,11
S PCo_7
I
.,,I
I/o bus (e)
I
I
Internal bus (16)
CRRI
[
Vcc Vss
U
S
CRRO
VAREF
(4 Kbyte
Data memory
m r 6- bit ti e /
A/ D
Program memory
,i
PC
TxD/PCo RxD/PC I o - ~ SCK/PC 2 o - = ~
-r'°j
} J Port A I
I
Read/write control
System control
S
PBo_7
PAo_7
RD
WR
ALE RESET
MODE 0
MODE I
Figure h Block diagram for the single-chip microcomputer
348
microprocessors and microsystems
Various kinds of addressing capabilities, as shown in Figures 3 and 4 and Table I, are available for data transfer and arithmetic and logical operation instructions. To support its 64k memory space in particular, its addressing functions against memories are quite powerful, including such functions as the base addressing, base-index addressing or autoincrement addressing.
Internal ROM
4096 byte x 8
4095 4096
Instructions
In the #PD781 I, there are a total of 150 different kinds of instruction, including the arithmetic and logical operation, tranfer and bit manipulation. Based on the static analysis of large amount of source code lines, lower occurrence instructions are combined into 2 byte instructions, allowing useful instructions to occupy fewer byte and execute faster. The #PD7811 further provides the instructions, such as the 16-bit arithmetic and logical operation, 16-bit shift rotation and multiply/divide, which are not provided by other single-chip microcomputers. A comparison of the #PD7811 with other single-chip microcomputers is shown in Table 2 by memory efficiency, operation time and number of source code lines. The processing items used for the above comparison are the basic items of I/O handler, character search, 16-bit shift, computed go to, two types of vector additions and block transfer as well as the 16-bit multiplication, each of which is widely used to compare the processing capability of 8-bit general-purpose microprocessors.
External memory 61184 byte x8
65279 65280 Internal RAM 224 byte x 8
65503 65504
Internal RAM ( standby ) 32 byte x 8
65535
Figure 2. Microcomputer memory space
The benchmarks in Table 2 represent the following: •
I Immediate } ~ /~ ~ Register indirect \ \ working register ~ _ _ "~ Register Register " ~
\
\
Internal program memory
----~--.....~ External
i
•
memory
B~os~index
IAccumulotorI ~ - - ~
~ , ~" /~
Register I / \ 1 Register ~
~ ' '~ Register ~
I 7,,______~_~--~ General I registers
\
Registerindirect Auto increment
•
Autodecrement
Working register direct ~
Direct ~
Internal data memory
I Special registers
• •
Figure 3. Addressing mode of transfer operation
IImmediateI ~ f~ ~
~
Working register Register Register " ~ JAccumulotorI - \ ' a L ~ Registerindirect • Auto increment Reg,ster ~"~ 1 Register ,~/Uotrkidng rr;gm:in:r
Internal program memory
•
External
•
memory
•
//~
AID converter internal data
General I registers
1
Special
registers
Figure 4. Addressing mode of arithmetic and logical operation
vol 6 no 7 september 1982
I/O handler ~1) - this is an interrupt-driven routine that fetches a character from a serial interface, stores it in software buffer and returns control to the main program character search (2) - searches a table of 40 characters in program memory for a specific character and generates the address of matched character or, upon failure, a zero address computed go to (3) - tests a control byte that has one true bit {the bit position determines which of eight table vectors is used for control transfer, in the test example; the true bit is set at the MSB) 16-bit shift (4) - shifts a 16-bit work right by five bit with zeros filling in from the left 16-bit vector addition {5) - adds two 20-dimensional vectors of 16-bit precision from external memory to generate a third 20-dimensional vector in internal memory 16-bit vector addition 16) - adds two 20-dimensional vectors of 8-bit precision from external memory to generate a third 20-dimensional vector in internal memory move block (7) - moves a block of 64 byte from external memory to internal memory 16-bit multiply (8) - multiplies two 16-bit unsigned binary numbers to produce a 32-bit product
memory
Almost all the data which indicate engine operating conditions are sent from the analogue sensors. It is thus necessary for the engine control system to convert these analogue signals into digital data as soon as possible and as accurately as possible. The #PD7811 has an 8-bit A/D converter on the chip in order to make direct interface with the analogue signals.
349
Table 1. Addressing modes The content of tire register
REGISTER
REGISTER ADDRESS
• OPERAND (REGISTER)
REGISTER INDIRECT
REGISTER ADDRESS
• ADDRESS (REGISTER PAIR)
•OPERAND
The content of the location whose address is in the register pair
AUTO INCREMENT
REGISTER ADDRESS
• ADDRESS (REGISTER PAIR)
~ OPERAND
Registerindirect addressing The content of the register pair is automatically incremented after the operand addressing.
• OPERAND
Register indirect addressing The content of the register pair is automatically decremented after the operand addressing.
•OPERAND
Register indirect addressing The content of the register pair is automatically incremented twice after the operand addressing.
t AUTO DECREMENT
REGISTER ADDRESS
REGISTER ADDRESS
+I
' • ADDRESS (REGISTE R~PAIR) t
DOUBLE AUTO INCREMENT
~)~
"
' @
-1
• ADDRESS (REGISTER, PAIR)
t DIRECT
ADDRESS
IMMEDIATE
OPERAND
WORKING REGISTER
V REGADDRESS
• OPERAND
The content of the location whose address is in the instruction In the instruction
• UPPER ADDRESS
(~) ----I~OPE RAN D
t
LOWER ADDRESS RELATIVE
ADDRESS (PROGRAM COUNTER)
~ ( ~ mll~OPE RAND
T
DISPLACEMENT . . . . . . . BASE
REGISTER ADDRESS
~ (~ - - • OPERAND
The content of the location whose address is the sum of the content of the base register and the displacement in the instruction
REGISTER ADDRESS
• BASE ADDRESS (BASE REGISTER)
~(~) ~ O P E R A N D
REGISTER ADDRESS
• INDEX ADDRESS' (INDEX REGISTER)
The content of the location whose address is the sum of the content of the base register and the displacement in the index register
Having eight analogue inputs, the converter can handle all the signals from air-flow and temperature sensors. The 8-bit converter adopts the successive approximation technique whose hardware consists of resistor ladder, sample-and-hold-capacitance and successive-approximation logics, as shown in Figure 5. By this technique, high-speed conversion of 50/Js and absolute accuracy of 1.5 LSB {least significant bit), including 0.5 LSB of quantization error, are obtained. Considering the possible noises which could be superimposed on the analogue lines, it is dangerous to use only
Y
recurrence and the highest accuracy. Temperature measurements, which contain air temperature, coolant temperature and catalizer temperature, do not require such frequency and accuracy of measurement. But because of noise in the engine room, the software filtering of the analogue signals is indispensable. Considering the characteristics of the value measured, the arithmetic average method or the mode method is suitable for the air-flow measurement and the Anologue inputs
•
arithmetic average method for several conversion results mode method in which the most frequent data is used as the true result exponential average method which has the advantage of large signal to noise ratios but has slower dynamic response
Among the many kinds of'analogue measurement, it is the air-flow measurement that requires the highest rate of
350
V~
A~C
'
'i
lIllIll;
one conversion result in the digital data processing as a true value of the analogue signal. In order to prevent misoperation due to noise, many kinds o f software filtering have been developed and the result o f the filtering is used as the true result of the conversion. Types of software filtering are shown below: • •
The content of the location whose address is the sum of the content of the program counter and the displacement in the instruction
• BASE ADDRESS (BASE REGISTER)
DISPLACEMENT -. BASE-INDEX
The content of the location whose upper address is in the Vector register and whose lower address is in the instruction
multiplexer [ Sompleand hold
eontro I
ladder J
Tap decoder
AV
'! ~
oppro• imation logic
-----F-T--
result
l
l.te~.ol bus
11
Figure 5. Block diagram o f A/D converter
microprocessors and microsystems
Table 2. Benchmark result Memory byte Benchmark*
Execution time [/Js) Z8
6801
7811 12MHz
8051 12MHz
7811
8051
14
22
14
16
21.8
22
18.5
48
16
19
21
18
298.8
406
468.5
11
32
19
14
67.8
74
17
22
13
9
19.5
55
Z8 8MHz
6801 4MHz
7811
8051
Z8
6801
11
12
5
8
730
9
10
11
9
73.5
127
6
16
11
8
41.5
23
8
18
7
7
26
37t/284:
36
44
404.8
886t/ 4854:
608.5 1504
15
22t/21:~
21
23
20
31t/204~
25
41
299.3
406t/ 265~
338.5 1184
10
19t/13~
14
20
485.5 2573
4
8
6
14
145
20
37
17
26
2369.5 6334
83
142t/ 1354:
92
115
7
9
14
12
27
214.8
516
8
31
49
32
49
59.0
54
144
216~-/ 1964=
172
218
1385.8
Total
Lines of source code
2419t/ 18774:
The benchmark results are taken from the authors' own performance comparison between the ~PD7811 and other products (previously undocumented) *External data memory beyond 256 addresslocation exponential average method is suitable for the temperature measurement. The A/D converter provides four conversion result registers and interrupts/A/D interrupt) in order to execute the software filtering. These four registers provide two operation modes. One is a channel-select mode which converts results from each analogue input; selection is programmable. The results are sequentially stored in the registers. This mode is useful for the arithmetic average method or the mode method of the air-flow measurement. The other mode is an automatic scanning mode. Here the A/D converter scans the upper or lower four analogue inputs and the conversion results are stored in the four conversion result registers respectively. This mode is useful to minimize the software overhead for analogue input selection. This A/D converter generates the A/D interrupt request as soon as the conversion results are transferred to the conversion result registers and tells the CPU when the conversion results in these registers are ready. Working continuously, the A/D converter always stores the last results in result registers. By using these registers and the A/D interrupt function, efficient data processing of the conversion results can be realized without any CPU wait time during the conversion.
Timer/counter Real-time and accurate control should be made over the injection time of the injector and the ignition timing of ignitor in order to improve the engine control precision. Thus, the pulse-output function must be performed automatically by the system hardware. The ~PD7811 fulfils such requirements for pulse processing using its built-in 16-bit timer/event counter and a pair of 8-bit interval timers. The 16-bit timer/event counter in
vol 6 no 7 september 1982
335
*The algorithms for each benchmark program are taken from those in an article in E/ectronics(27 May 1976). The authors also referred for the Motorola 6809 performance comparison, which contains the source programs for those bench marks. tExternal data memory up to 256 address location particular is designed to provide sophisticated yet highly accurate pulse output. As shown in Figure 6, it is composed of a 16-bit upcounter, two 16-bit compare registers, two 16-bit comparators, a 16-bit capture register and a pulse control logic. The latter is specially provided with two independent pulseoutput lines. It is therefore possible to execute simultaneous control by a single/~PD7811 over both injection and ignition. The 16-bit up-counter is continually compared with either the compare register 0 or the compare register 1. Whenever equality is detected, the pulse output is set or reset according to the pulse control logic. So by this 16-bit timer/event counter, any frequency, phase, pulse position or pulse width can be controlled. In automotive engine control, the output timing and pulse width of the pulse signals for ignitor and/or injector are generally obtained through complicated data processing based on the data from the analogue sensors, such as A/D conversion, table took-up, interpolation and calibration. The software processing required for pulse output can be i ,o,.... ,0o
/
Infernal clock
I
Q -,
]
up counter ,J
!
t
,
~
~
I=::'.,o,,.,., I Intorno~ bus
- - q ,2:7' ~
t
co,
J
i
Figure 6. Block diagram of 16-bit timer~event counter
351
performed simply be setting the calculation result to the 16-bit compare register; otherwise the controls for such a purpose are automatically done by the hardware. The #PD7811 is equipped to do this.
Serial communication interface Automotive control by microcomputer is expected to become more versatile, e.g. it covers the transmission, brake or other power transmission systems, besides the engine and dashboard control. To successfully deal with such demands for higher level functions of the general control system, the distributed control system, which may be based on multiprocessor configuration, provided for various control items by means of the serial lines, is considered better than the central control system in regard to the performance and cost as well as to protection against system failure. The #PD7811 's built-in serial communication interface caters for any extensively distributed control system expected in the near future. This serial communication interface provides double buffer registers for receipt and transmit operations. It can be used in three different modes: asynchronous mode, where both the bit- and character-synchronization are affected by the start bit; synchronous mode, for character synchronization to be made by software; and I[O interface
Table 3. Interrupt sources
mode, to transfer data which are synchronized with eight serial clock pulses. In asynchronous mode, especially according to the double-buffered data paths, the transmit and receipt operation can be independently performed. Also character length, the number of stop bit and parity assignments can be selected by software. The serial communication interface can insert an even or odd parity bit prior to the stop bit in the transmit operation. Also in the receipt operation, it always checks the parity error, framing error and overrun error. By using the serial communication interface, a reliable distributed system can be realized.
Interrupt Each peripheral operates independently of the CPU. Thus it is important for efficient control to synchronize the operation of the peripherals with the CPU. The #PD7811 has a powerful interrupt capability, as shown in Table 3. Eleven interrupt sources are provided and each of them can be independently masked by software. They are divided into two groups. One group contains three external interrupts including nonmaskable interrupt. The other contains eight internal interrupts, namely one from the A/D converter, three from the 16-bit timer/event counter, two from the two 8-bit interval timers and two from serial communication interface. These interrupt sources are classified into six priority levels, and organically associated with the CPU.
APPLICABILITY TO ENGINE CONTROL Level
Source
Comment
IRQO
NMI [nonmaskable interrupt)
External falling edge triggered Nonmaskable interrupt
IRQ1
INTT0
Timer 0 interrupt from 8-bit interval timer 0
INTT1
Timer 1 interrupt from 8-bit interval timer 1
INT1
External rising edge triggered
I NT2
External falling edge triggered
INTEO
CR0 compare interrupt from 16-bit timer/event counter
INTE1
CR1 compare interrupt from 16-bit timer/event counter
I RQ2
I RQ3
The applicability of the #PD7811 to automotive applications, as compared with other microcomputers, is shown in Figure 7. The comparison is made on table look-up and interpolation for engine control. The x and y axes indicate the processing time and the number of memory bytes required for processing. The performance of the /JPD7811 is much improved as the plotted dot is shifted down to the left. The data processing used for the comparison are practically useful to find the air:fuel ratio or spark timing from two kinds of data; viz, the air-flow and the engine speed. This processing picks up four table data, namely f(a,b), f(o+l ,b), f(a,b+l ) and f(a+l ,b+l ), which are used in the two-dimensional interpolation, from the two-dimensional table based on the two input parameters x and y. Then the final result f(x,y) is obtained by the two-dimensional interpolation as shown in Figure 8. This processing contains three kinds of processing.
Engine control 6801 o
130 120
IRQ4
INTEIN INTAD
Capture interrupt from 16-bit timer/event counter A/D converter interrupt
8051 o
IIO >, I00
Z8 o
IE
IRQ5
INTSR INTFR
Receive interrupt from serial communication interface Transmit interrupt from serial communication interface
T h e r e are 11 i n t e r r u p t sources and six p r i o r i t y levels. Individual request mask capability except NMI
352
80
p.PD7811 (12 MHz)
%
70 0
°-"-#PD7811 (10 MHz)
05
I0
15
20
I .... 25
L_ 50
J 55
Speed (ms)
Figure 7. Comparison ot the pertormance ot the 1~D 7811 with other commercially available 8-bit single-chip microcomputers, namely the 6801, 8051 and Z8 machines
microprocessors and microsvstems
• as the preprocessing for the look-up of the twodimensional table has 4-bit index for the x-axis, 4-bit for the y-axis, the first process converts an 8-bit parameter into a 4-bit index • the second process picks up the data from the table by the 4-bit x-axis index and 4-bit y-axis index • the third processing executes the one-dimensional interpolation according to the following formula:
g(x) = g(a) + (g(b) -g(a))(x-a)/(b-a) The first process must be executed twice to obtain two 4-bit indexes from two 8-bit parameters. The second process must be executed four times leaving the four items of data in preparation for the two-dimensional interpolation as shown in Figure 6 and the third process must be calculated three times because the two-dimensional interpolation requires three one-dimensional interpolations in one equation. The computed result shows the ~PD7811 to be several
+I)
times more efficient than the other single-chip microcomputers, as shown in Figure 7. Such a superior performance can be attributed to the effects of base-index addressing on the two-dimensional table look-up or those of the 8 x 8-bit multiply and 16 x 8-bit divide instructions used in the interpolation.
CONCLUSIONS The p.PD7811 is a single-chip microcomputer which has been particularly developed for automotive engine control using NMOS technology. It is equipped for analogue signal processing, pulse signal processing, high-speed data processing and other functions needed for engine control. Microcomputer engine control has evolved into control by single-chip microcomputers because of the general necessity for compaction and the need for highly reliable and low cost engine control. Further advances in this single-chip microcomputer system for sophisticated engine control are planned. These include improving the operating temperature/power supply voltage with noise-immune CMOS device, improving the resolusion/accuracy of the A/D converter, greater onchip memory and serial data interface suited for distributed systems.
F(x,y) Y
sEngi p ene d
/b+l
/
ACKNOWLEDGEMENTS ]
E"
~l,b+l) X / "F(oq,b)
Index (4°bit)
\\ Airflow (8-bit) X
Figure 8. Mapping of the injection time
vol 6 no 7 september 1982
The authors wish to thank Masanori Ariga, Hideyo Kanayama and Minoru Matsuda for their helpful discussion. The authors are also indebted to Tamotsu Goto, Mitsno Sakai, Masashi Endo and Kenji Kani for their constant encouragement and efforts throughout the project.
BIBLIOGRAPHY Matney, R, Nuckols, ] and Wand, M 'An approach to a standard engine management system for 1983 and beyond' SAE Paper 800470 (February 1980) Jones, T O and Barnicoat, G D 'Automotive microprocessor' SAE Paper 780860 (September 1978)
353
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354
microprocessors and microsystem
microprocessors automotive enginecontrol The rapid growth of LSI technology keeps its pace year after year and so the microcomputer has attained higher functionality yet lower cost because of the continuous improvements in chip integration. The current microcomputers can be categorized into the two: one for the general-purpose applications and the other for single-chip microcomputers. In line with the continued improvement in performance, some general-purpose microprocessors have already exceeded the functionality of minicomputers. At the same time, the larger onchip memory, faster CPU and onchip peripherals of single-chip microcomputers are no longer a illusion, thanks to increased integration. It allows the single-chip microcomputer to act as a higher-performance controller. In line with this trend the single-chip microcomputer, /aPD7811, has been developed for automotive engine control. In general, a microcomputer for total engine control system requires the following functions: • high quality A/D converter • pulse-output handling capability such as flexible pulseposition and pulse-width modulation • high speed data processing capability and sophisticated peripheral control for program efficiency Present technology has made it possible to integrate all these necessary functional blocks required for total engine control as well as high-level bit processing, large memory capability and other essential functions onto a single chip. Plant, 1753 5himonumabe, Nakahaka-ku, Kawasaki 211, Japan This paper is based on a presentation given at ISATA 81, the
Nippon Electric Company Ltd, Tamagawa
International Symposium on Automotive technology and Automation, in Stockholm, Sweden. The proceedings of ISATA 81 are available from Automotive Automation Ltd, Croydon, UK
v o / 6 n o 7september 1982
SYSTEM FEATURES The microcomputer was designed to have more onchip peripherals and an instruction set which is better suited to engine control applications.
Peripheral functions In microcomputer-based engine control optimized air:fuel ratio and spark timing are calculated from various engine parameters and environmental parameters such as air-flow and engine speed. Fuel injectors and ignitors are controlled with series of pulse signals whose output timing and width are based on the above calculations. However, in general, engine control systems have the two problems. Firstly. since almost all parameters, such as air-flow and air-temperature which are derived from analogue sensors, needed for engine control must be converted to digital data. Secondly, an accurate pulse-output capability is necessary since pulse generation must be precisely controlled, based on the calculation results of pulse-output timing and pulse width. In order to control the pulse position and the pulse width precisely, the pulse output capability must be free from software output control. To solve these problems, the pPD7811 has been equipped with an 8-bit converter, 16-bit timer]event counter and a pair of 8-bit interval timers. The onchip A/D converter has eight analogue inputs so most of the analogue signals from various sensors can be handled without additional A/D LSI chips. The 16-bit timer/event counter is designed for flexible pulse-position and pulse-width modulation. By using this 16-bit timer/ event counter, pulses for the actuator control can be easily and precisely generated. On the other hand, existing engine control systems use many dedicated LSI chips, for A/D conversion and pulseoutput control. In such systems, which comprise several LSI chips, a different problem arises, because each LSI chips must be linked by a parallel databus. Multichip systems in a strong noise environment, such as an engine room, may be in danger of misoperation because various noises are induced on the databus of the control system. Thus such engine control systems essentially contain problems of both reliability and security. Since the IaPD7811 makes a direct interface between the CPU and the various analogue sensors and actuators, the engine control system itself is free from noise transmitted over the databus. This results in improvement of the
0141-9331[82[070347--07 $03.00 © 1982 Butterworth & Co (Publishers) Ltd
347
reliability and the security of the engine control system. In addition to these facilities, the microcomputer also contains a serial communication interface in order to match a distributed control system which will come into use in near future. Increasing the control items of an automative management system to include not only dashboard and engine control but also transmission and suspension makes a distributed system even more vital. The importance el serial data transfer is thus increased.
executed within 8 #s, or a divide operation ol 16 x S-bii in 14/Js. The bit manipulation instructions of bit setting, resetting or testing are improved. Thus and I/O line can be selectively read, set or reset with a single instruction ~vithout having to retain an IjO pin image in software and various flags to hold the controlled status can be readily set up in memory.
ARCHITECTURE Due to the NMOS process, the/IPD781 I contains the functional blocks such as 4k of ROM, 256 byte of RAM, 44 I/O lines, an 8-bit A/D converter, 16-bit timer/event counter, two 8-bit interval timers and serial communication interface on the single chip as shown in Figure 1. Further, the 8-bit single-chip microcomputer has 16-bit operation instructions, including those for multiply and divide table look-up instructions and bit-manipulation instructions. In addition to the stand-alone system configuration, tile bus-compatibility of the ~PD7811 with 8085A enables building up of a large-scale control system with memories and other LSI chips.
I n s t r u c t i o n set In the control system, since the air:fuel ratio and spark timing should be controlled in real time, the CPU has to calculate the pulse-output timing and pulse width for the injector and ignitor at a high speed. The output timing and width of pulses can generally be got by looking up in the two-dimensional table which gives two different types of data. This data is converted from analogue to digital, and by two-dimensional interpolation and other calibrations. Accordingly, to implement the high-speed processing, the instruction cycle must not only be shortened, but there must an instruction set provided that is more suitable for data processing in the above, such as in interpolation, etc. The instruction cycle time of the/JPD7811 is 1 #s. It has not only a short processing time, but also contains an powerful instruction set with such functions as 16-bit data transfer, 16-bit arithmetic and logical operations and table look-up or multiply/divide in order to handle data more efficiently. The multiply operation of 8 x 8-bit can be
Memory
and addressing
The single-chip microcomputer has a total of 64k of memory space in which the 4k internal ROM, 256 byte internal RAM and 60k external expandibl¢ memory are assigned (Figure 2). Accordingly, a space of 60k out of the 64k memory space, except the internal ROM area, can be used either for program memory or data memory. XI
N., INTI
X2
VDD
Address bus Interrupt
INT2/TI INC/DEC SP
Serial I/0
B
I
TI/PG s o - ~
8-bit interval
V
timer O, I
EA
TOIPC 4
I
ClIPC5 ~ COO/PC ~
6COl I PC 7
I
AVcc ~ VASS
L E C A
H D
H'
L'
D' B' V'
E' C' A'
(,256 byte)
EA'
..q
event counter
converter
ANo 7
",6 instantaneous I register _ J
CRR2 CRR3
Instantaneous
I
I
II PFo_7
S PDo_7
.,11
S PCo_7
I
.,,I
I/o bus (e)
I
I
Internal bus (16)
CRRI
[
Vcc Vss
U
S
CRRO
VAREF
(4 Kbyte
Data memory
m r 6- bit ti e /
A/ D
Program memory
,i
PC
TxD/PCo RxD/PC I o - ~ SCK/PC 2 o - = ~
-r'°j
} J Port A I
I
Read/write control
System control
S
PBo_7
PAo_7
RD
WR
ALE RESET
MODE 0
MODE I
Figure h Block diagram for the single-chip microcomputer
348
microprocessors and microsystems
Various kinds of addressing capabilities, as shown in Figures 3 and 4 and Table I, are available for data transfer and arithmetic and logical operation instructions. To support its 64k memory space in particular, its addressing functions against memories are quite powerful, including such functions as the base addressing, base-index addressing or autoincrement addressing.
Internal ROM
4096 byte x 8
4095 4096
Instructions
In the #PD781 I, there are a total of 150 different kinds of instruction, including the arithmetic and logical operation, tranfer and bit manipulation. Based on the static analysis of large amount of source code lines, lower occurrence instructions are combined into 2 byte instructions, allowing useful instructions to occupy fewer byte and execute faster. The #PD7811 further provides the instructions, such as the 16-bit arithmetic and logical operation, 16-bit shift rotation and multiply/divide, which are not provided by other single-chip microcomputers. A comparison of the #PD7811 with other single-chip microcomputers is shown in Table 2 by memory efficiency, operation time and number of source code lines. The processing items used for the above comparison are the basic items of I/O handler, character search, 16-bit shift, computed go to, two types of vector additions and block transfer as well as the 16-bit multiplication, each of which is widely used to compare the processing capability of 8-bit general-purpose microprocessors.
External memory 61184 byte x8
65279 65280 Internal RAM 224 byte x 8
65503 65504
Internal RAM ( standby ) 32 byte x 8
65535
Figure 2. Microcomputer memory space
The benchmarks in Table 2 represent the following: •
I Immediate } ~ /~ ~ Register indirect \ \ working register ~ _ _ "~ Register Register " ~
\
\
Internal program memory
----~--.....~ External
i
•
memory
B~os~index
IAccumulotorI ~ - - ~
~ , ~" /~
Register I / \ 1 Register ~
~ ' '~ Register ~
I 7,,______~_~--~ General I registers
\
Registerindirect Auto increment
•
Autodecrement
Working register direct ~
Direct ~
Internal data memory
I Special registers
• •
Figure 3. Addressing mode of transfer operation
IImmediateI ~ f~ ~
~
Working register Register Register " ~ JAccumulotorI - \ ' a L ~ Registerindirect • Auto increment Reg,ster ~"~ 1 Register ,~/Uotrkidng rr;gm:in:r
Internal program memory
•
External
•
memory
•
//~
AID converter internal data
General I registers
1
Special
registers
Figure 4. Addressing mode of arithmetic and logical operation
vol 6 no 7 september 1982
I/O handler ~1) - this is an interrupt-driven routine that fetches a character from a serial interface, stores it in software buffer and returns control to the main program character search (2) - searches a table of 40 characters in program memory for a specific character and generates the address of matched character or, upon failure, a zero address computed go to (3) - tests a control byte that has one true bit {the bit position determines which of eight table vectors is used for control transfer, in the test example; the true bit is set at the MSB) 16-bit shift (4) - shifts a 16-bit work right by five bit with zeros filling in from the left 16-bit vector addition {5) - adds two 20-dimensional vectors of 16-bit precision from external memory to generate a third 20-dimensional vector in internal memory 16-bit vector addition 16) - adds two 20-dimensional vectors of 8-bit precision from external memory to generate a third 20-dimensional vector in internal memory move block (7) - moves a block of 64 byte from external memory to internal memory 16-bit multiply (8) - multiplies two 16-bit unsigned binary numbers to produce a 32-bit product
memory
Almost all the data which indicate engine operating conditions are sent from the analogue sensors. It is thus necessary for the engine control system to convert these analogue signals into digital data as soon as possible and as accurately as possible. The #PD7811 has an 8-bit A/D converter on the chip in order to make direct interface with the analogue signals.
349
Table 1. Addressing modes The content of tire register
REGISTER
REGISTER ADDRESS
• OPERAND (REGISTER)
REGISTER INDIRECT
REGISTER ADDRESS
• ADDRESS (REGISTER PAIR)
•OPERAND
The content of the location whose address is in the register pair
AUTO INCREMENT
REGISTER ADDRESS
• ADDRESS (REGISTER PAIR)
~ OPERAND
Registerindirect addressing The content of the register pair is automatically incremented after the operand addressing.
• OPERAND
Register indirect addressing The content of the register pair is automatically decremented after the operand addressing.
•OPERAND
Register indirect addressing The content of the register pair is automatically incremented twice after the operand addressing.
t AUTO DECREMENT
REGISTER ADDRESS
REGISTER ADDRESS
+I
' • ADDRESS (REGISTE R~PAIR) t
DOUBLE AUTO INCREMENT
~)~
"
' @
-1
• ADDRESS (REGISTER, PAIR)
t DIRECT
ADDRESS
IMMEDIATE
OPERAND
WORKING REGISTER
V REGADDRESS
• OPERAND
The content of the location whose address is in the instruction In the instruction
• UPPER ADDRESS
(~) ----I~OPE RAN D
t
LOWER ADDRESS RELATIVE
ADDRESS (PROGRAM COUNTER)
~ ( ~ mll~OPE RAND
T
DISPLACEMENT . . . . . . . BASE
REGISTER ADDRESS
~ (~ - - • OPERAND
The content of the location whose address is the sum of the content of the base register and the displacement in the instruction
REGISTER ADDRESS
• BASE ADDRESS (BASE REGISTER)
~(~) ~ O P E R A N D
REGISTER ADDRESS
• INDEX ADDRESS' (INDEX REGISTER)
The content of the location whose address is the sum of the content of the base register and the displacement in the index register
Having eight analogue inputs, the converter can handle all the signals from air-flow and temperature sensors. The 8-bit converter adopts the successive approximation technique whose hardware consists of resistor ladder, sample-and-hold-capacitance and successive-approximation logics, as shown in Figure 5. By this technique, high-speed conversion of 50/Js and absolute accuracy of 1.5 LSB {least significant bit), including 0.5 LSB of quantization error, are obtained. Considering the possible noises which could be superimposed on the analogue lines, it is dangerous to use only
Y
recurrence and the highest accuracy. Temperature measurements, which contain air temperature, coolant temperature and catalizer temperature, do not require such frequency and accuracy of measurement. But because of noise in the engine room, the software filtering of the analogue signals is indispensable. Considering the characteristics of the value measured, the arithmetic average method or the mode method is suitable for the air-flow measurement and the Anologue inputs
•
arithmetic average method for several conversion results mode method in which the most frequent data is used as the true result exponential average method which has the advantage of large signal to noise ratios but has slower dynamic response
Among the many kinds of'analogue measurement, it is the air-flow measurement that requires the highest rate of
350
V~
A~C
'
'i
lIllIll;
one conversion result in the digital data processing as a true value of the analogue signal. In order to prevent misoperation due to noise, many kinds o f software filtering have been developed and the result o f the filtering is used as the true result of the conversion. Types of software filtering are shown below: • •
The content of the location whose address is the sum of the content of the program counter and the displacement in the instruction
• BASE ADDRESS (BASE REGISTER)
DISPLACEMENT -. BASE-INDEX
The content of the location whose upper address is in the Vector register and whose lower address is in the instruction
multiplexer [ Sompleand hold
eontro I
ladder J
Tap decoder
AV
'! ~
oppro• imation logic
-----F-T--
result
l
l.te~.ol bus
11
Figure 5. Block diagram o f A/D converter
microprocessors and microsystems
Table 2. Benchmark result Memory byte Benchmark*
Execution time [/Js) Z8
6801
7811 12MHz
8051 12MHz
7811
8051
14
22
14
16
21.8
22
18.5
48
16
19
21
18
298.8
406
468.5
11
32
19
14
67.8
74
17
22
13
9
19.5
55
Z8 8MHz
6801 4MHz
7811
8051
Z8
6801
11
12
5
8
730
9
10
11
9
73.5
127
6
16
11
8
41.5
23
8
18
7
7
26
37t/284:
36
44
404.8
886t/ 4854:
608.5 1504
15
22t/21:~
21
23
20
31t/204~
25
41
299.3
406t/ 265~
338.5 1184
10
19t/13~
14
20
485.5 2573
4
8
6
14
145
20
37
17
26
2369.5 6334
83
142t/ 1354:
92
115
7
9
14
12
27
214.8
516
8
31
49
32
49
59.0
54
144
216~-/ 1964=
172
218
1385.8
Total
Lines of source code
2419t/ 18774:
The benchmark results are taken from the authors' own performance comparison between the ~PD7811 and other products (previously undocumented) *External data memory beyond 256 addresslocation exponential average method is suitable for the temperature measurement. The A/D converter provides four conversion result registers and interrupts/A/D interrupt) in order to execute the software filtering. These four registers provide two operation modes. One is a channel-select mode which converts results from each analogue input; selection is programmable. The results are sequentially stored in the registers. This mode is useful for the arithmetic average method or the mode method of the air-flow measurement. The other mode is an automatic scanning mode. Here the A/D converter scans the upper or lower four analogue inputs and the conversion results are stored in the four conversion result registers respectively. This mode is useful to minimize the software overhead for analogue input selection. This A/D converter generates the A/D interrupt request as soon as the conversion results are transferred to the conversion result registers and tells the CPU when the conversion results in these registers are ready. Working continuously, the A/D converter always stores the last results in result registers. By using these registers and the A/D interrupt function, efficient data processing of the conversion results can be realized without any CPU wait time during the conversion.
Timer/counter Real-time and accurate control should be made over the injection time of the injector and the ignition timing of ignitor in order to improve the engine control precision. Thus, the pulse-output function must be performed automatically by the system hardware. The ~PD7811 fulfils such requirements for pulse processing using its built-in 16-bit timer/event counter and a pair of 8-bit interval timers. The 16-bit timer/event counter in
vol 6 no 7 september 1982
335
*The algorithms for each benchmark program are taken from those in an article in E/ectronics(27 May 1976). The authors also referred for the Motorola 6809 performance comparison, which contains the source programs for those bench marks. tExternal data memory up to 256 address location particular is designed to provide sophisticated yet highly accurate pulse output. As shown in Figure 6, it is composed of a 16-bit upcounter, two 16-bit compare registers, two 16-bit comparators, a 16-bit capture register and a pulse control logic. The latter is specially provided with two independent pulseoutput lines. It is therefore possible to execute simultaneous control by a single/~PD7811 over both injection and ignition. The 16-bit up-counter is continually compared with either the compare register 0 or the compare register 1. Whenever equality is detected, the pulse output is set or reset according to the pulse control logic. So by this 16-bit timer/event counter, any frequency, phase, pulse position or pulse width can be controlled. In automotive engine control, the output timing and pulse width of the pulse signals for ignitor and/or injector are generally obtained through complicated data processing based on the data from the analogue sensors, such as A/D conversion, table took-up, interpolation and calibration. The software processing required for pulse output can be i ,o,.... ,0o
/
Infernal clock
I
Q -,
]
up counter ,J
!
t
,
~
~
I=::'.,o,,.,., I Intorno~ bus
- - q ,2:7' ~
t
co,
J
i
Figure 6. Block diagram of 16-bit timer~event counter
351
performed simply be setting the calculation result to the 16-bit compare register; otherwise the controls for such a purpose are automatically done by the hardware. The #PD7811 is equipped to do this.
Serial communication interface Automotive control by microcomputer is expected to become more versatile, e.g. it covers the transmission, brake or other power transmission systems, besides the engine and dashboard control. To successfully deal with such demands for higher level functions of the general control system, the distributed control system, which may be based on multiprocessor configuration, provided for various control items by means of the serial lines, is considered better than the central control system in regard to the performance and cost as well as to protection against system failure. The #PD7811 's built-in serial communication interface caters for any extensively distributed control system expected in the near future. This serial communication interface provides double buffer registers for receipt and transmit operations. It can be used in three different modes: asynchronous mode, where both the bit- and character-synchronization are affected by the start bit; synchronous mode, for character synchronization to be made by software; and I[O interface
Table 3. Interrupt sources
mode, to transfer data which are synchronized with eight serial clock pulses. In asynchronous mode, especially according to the double-buffered data paths, the transmit and receipt operation can be independently performed. Also character length, the number of stop bit and parity assignments can be selected by software. The serial communication interface can insert an even or odd parity bit prior to the stop bit in the transmit operation. Also in the receipt operation, it always checks the parity error, framing error and overrun error. By using the serial communication interface, a reliable distributed system can be realized.
Interrupt Each peripheral operates independently of the CPU. Thus it is important for efficient control to synchronize the operation of the peripherals with the CPU. The #PD7811 has a powerful interrupt capability, as shown in Table 3. Eleven interrupt sources are provided and each of them can be independently masked by software. They are divided into two groups. One group contains three external interrupts including nonmaskable interrupt. The other contains eight internal interrupts, namely one from the A/D converter, three from the 16-bit timer/event counter, two from the two 8-bit interval timers and two from serial communication interface. These interrupt sources are classified into six priority levels, and organically associated with the CPU.
APPLICABILITY TO ENGINE CONTROL Level
Source
Comment
IRQO
NMI [nonmaskable interrupt)
External falling edge triggered Nonmaskable interrupt
IRQ1
INTT0
Timer 0 interrupt from 8-bit interval timer 0
INTT1
Timer 1 interrupt from 8-bit interval timer 1
INT1
External rising edge triggered
I NT2
External falling edge triggered
INTEO
CR0 compare interrupt from 16-bit timer/event counter
INTE1
CR1 compare interrupt from 16-bit timer/event counter
I RQ2
I RQ3
The applicability of the #PD7811 to automotive applications, as compared with other microcomputers, is shown in Figure 7. The comparison is made on table look-up and interpolation for engine control. The x and y axes indicate the processing time and the number of memory bytes required for processing. The performance of the /JPD7811 is much improved as the plotted dot is shifted down to the left. The data processing used for the comparison are practically useful to find the air:fuel ratio or spark timing from two kinds of data; viz, the air-flow and the engine speed. This processing picks up four table data, namely f(a,b), f(o+l ,b), f(a,b+l ) and f(a+l ,b+l ), which are used in the two-dimensional interpolation, from the two-dimensional table based on the two input parameters x and y. Then the final result f(x,y) is obtained by the two-dimensional interpolation as shown in Figure 8. This processing contains three kinds of processing.
Engine control 6801 o
130 120
IRQ4
INTEIN INTAD
Capture interrupt from 16-bit timer/event counter A/D converter interrupt
8051 o
IIO >, I00
Z8 o
IE
IRQ5
INTSR INTFR
Receive interrupt from serial communication interface Transmit interrupt from serial communication interface
T h e r e are 11 i n t e r r u p t sources and six p r i o r i t y levels. Individual request mask capability except NMI
352
80
p.PD7811 (12 MHz)
%
70 0
°-"-#PD7811 (10 MHz)
05
I0
15
20
I .... 25
L_ 50
J 55
Speed (ms)
Figure 7. Comparison ot the pertormance ot the 1~D 7811 with other commercially available 8-bit single-chip microcomputers, namely the 6801, 8051 and Z8 machines
microprocessors and microsvstems
• as the preprocessing for the look-up of the twodimensional table has 4-bit index for the x-axis, 4-bit for the y-axis, the first process converts an 8-bit parameter into a 4-bit index • the second process picks up the data from the table by the 4-bit x-axis index and 4-bit y-axis index • the third processing executes the one-dimensional interpolation according to the following formula:
g(x) = g(a) + (g(b) -g(a))(x-a)/(b-a) The first process must be executed twice to obtain two 4-bit indexes from two 8-bit parameters. The second process must be executed four times leaving the four items of data in preparation for the two-dimensional interpolation as shown in Figure 6 and the third process must be calculated three times because the two-dimensional interpolation requires three one-dimensional interpolations in one equation. The computed result shows the ~PD7811 to be several
+I)
times more efficient than the other single-chip microcomputers, as shown in Figure 7. Such a superior performance can be attributed to the effects of base-index addressing on the two-dimensional table look-up or those of the 8 x 8-bit multiply and 16 x 8-bit divide instructions used in the interpolation.
CONCLUSIONS The p.PD7811 is a single-chip microcomputer which has been particularly developed for automotive engine control using NMOS technology. It is equipped for analogue signal processing, pulse signal processing, high-speed data processing and other functions needed for engine control. Microcomputer engine control has evolved into control by single-chip microcomputers because of the general necessity for compaction and the need for highly reliable and low cost engine control. Further advances in this single-chip microcomputer system for sophisticated engine control are planned. These include improving the operating temperature/power supply voltage with noise-immune CMOS device, improving the resolusion/accuracy of the A/D converter, greater onchip memory and serial data interface suited for distributed systems.
F(x,y) Y
sEngi p ene d
/b+l
/
ACKNOWLEDGEMENTS ]
E"
~l,b+l) X / "F(oq,b)
Index (4°bit)
\\ Airflow (8-bit) X
Figure 8. Mapping of the injection time
vol 6 no 7 september 1982
The authors wish to thank Masanori Ariga, Hideyo Kanayama and Minoru Matsuda for their helpful discussion. The authors are also indebted to Tamotsu Goto, Mitsno Sakai, Masashi Endo and Kenji Kani for their constant encouragement and efforts throughout the project.
BIBLIOGRAPHY Matney, R, Nuckols, ] and Wand, M 'An approach to a standard engine management system for 1983 and beyond' SAE Paper 800470 (February 1980) Jones, T O and Barnicoat, G D 'Automotive microprocessor' SAE Paper 780860 (September 1978)
353
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microprocessors and microsystem