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Take advantage of thermal effects to solve circuit-design problems
pp 25-36
Miller, R M 'Plug-in module adds FORTHlanguage and assembler to a handheld computer' Hewlett-Packard J. Vol 35 No 7 (July 1984) pp 37-40 The HP-71 B is a handheld computer from Hewlett-Packard. This issue of Hewlett-Packard Journal is completely given over to describing hardware of and software for the H P-71 B. Programmable in BASIC,the device can be used to control instruments and peripherals, communicate with other computers and operate as an algebraic calculator. Wechsler introduces the HP-71B. She describes the display and keyboard, the file management and file security systems and issues of customization and key redefinition that arose in its design. Customization and expansion procedures are based on an 'open machine' concept, which is explained in the documentation that comes with the HP-71B. Meyers concentrates on the socalled 'soft memory configuration' of the computer. This means that some devices occupying the address space do not have fixed locations -their addresses are assigned to them by the CPU. Meyers shows how this works, and deals with the methods used to extend RAM, to accommodate new RAM plug-ins, and to remove RAM modules nondestructively so that the RAM is ROM like with an independent file chain similar to plug-in ROMs. Configuration of memory-mapped I/O devices, and configuration of everything in daisychain order after addresses have been assigned, are also touched on. The electronics system for the HP-71B is based on seven custom CMOS integrated circuits. Dickies explains how these fit with the rest of the system hardware. He then goes on to describe the bus architecture and operating modes of the CPU. Lindberg deals exclusively with hardware. He presents the H P71B piece bypiece, and includesan account of various plug-in modules and peripherals for use with the device. Blascow and Donnelly have tackled the specific problem of fitting
vol 8 no 8 october 1984
observed data to a mathematical model and finding optimum values for a multivariable function. They used three separate BASICprograms, and based their approach on the Fletcher-Powell method of finding local minima in a function of k variables. Problems with error handling and software testing are summarized. The standard numerical function set of the HP-71B can be extended with the plug-in Math Pac ROM module. Grodd and Patton take a close look at some of the functions of Math Pac, and describe how complex matrix operations, matrix I/O operations, root finding and integration are handled. An algorithm for finding polynomial roots is explained and evaluated. Another plug-in ROM for the HP71B is the FORTH/assembler Pac. The 48 kbyte ROM provides a FORTH kernel, an assembler written in FORTH, an editor written in BASIC and a remote keyboard function. The authors justify the choice of FORTH as an add-on language, and discuss various aspects of the design of the Pac.
Design Adams, l H 'SC84 microcomputer' Electron. Wireless World Vol 90 No 1582 (July 1984) pp 31-34, 64-66 A monochrome VDU circuit for a Z80-based microcomputer is illustrated. The design uses Hitachi VDU controllers with light pen register and interlaced video. It relies on memory mapping and pipelining techniques for its operation and synchronization. Either a monitor or a monochrome television set can be used for display. Adams shows how to connect a monitor to the SC84. Keyboard and parallel I/O interfacing are also discussed. This is the third in a series of articles on the SC84.
The SC84 microcomputer is designed as a series of Eurocards plugged into a common backplane. Adams lists suppliers of frames into which these cards may be fitted. He gives guidelines for setting up a system to meet specific requirements. Also included are notes on connecting various disc drives and on syntax in MCOS, the computer's machine code operating system.
Ewen, G J and Adams, M l 'Microcomputer interfacing: an asynchronous serial communications interface' Lab. Pract. Vol 33 No 9 (September 1984) pp 112-113 An asynchronous serial communications interface has been designed for use with the Apple II and Apple lie microcomputers. The interface can be operated in RS232C or 2 0 m A current loop mode at switch-selectable baud rates. Details of the circuit and the operation of the interface are given. Also included is a 6502 machine code routine which allows the Apple to operate as a terminal in full-duplex mode. A typical RS232C autoloopback configuration is shown.
Penfold, R A 'Parallel to serial converter' Pract. Electron. Vol 20 No 9 (September 1984) pp 17-20 Because RS232C and RS423 ports handle serial data, it is not normally possible to drive directly such things as relays and D/A converters or to read directly switches, A/D converters and similar devices. Penfold has developed a parallel-to-serial converter which allows the use of an RS232C or RS423 port as a parallel port having eight input and eight output lines. The converter is shown first as a block diagram and then as a circuit diagram. The PCB layout of the unit is also given, along with the component arrangement. Details of the construction and operating needs of the device are included.
Adams, J H 'SC84 microcomputer' Electron. Wireless World Vol 90 No 1583 (July 1984) pp 51-53, 63
Williams, J 'Take advantage of thermal effects to solve circuit-design problems'
441
EDN Vol 29 No 13 (28 June 1984) pp 239-248 Instead of trying to eliminate or compensate for thermal parasitics in circuits, designers can use them to solve measurement and control problems. As an example Williams shows how, in a precision temperature controller for a small oven, a resistor switch in series with the thermistor can generate a step input for testing the circuit's response. Another application for temperature control is a thermal RMS/DC converter. Williams proposes a circuit that overcomes the drawbacks associated with the usual conversion process of rectification and averaging. Yet another example is the thermal flowmeter for low fluid flow rates, or for measuring air or gas flow. The final circuit in the article is for a thermally stabilized oscillator.
Applications Ewins, A l 'Micro-controlled cassette recorder - - 2'Electron. Wireless World Vo190 No 1582 (July 1984) pp 61-62, 67 Three sources of error in high~ speed digital multichannel designs for recording serial data from the output of a microcomputer are imperfections in tape quality, dirty tapeheads and indifferent transport of the tape across the head. A technique that is far less sensitive to these sources of error, says Ewins, is frequency shift keying (FSK). He presents circuit diagrams of an FSK modulator and demodulator. Based on Signetics designs, the circuits have been augmented by Ewins to overcome some of the problems associated with the high-frequency pre-emphasis circuitry. Various components in each circuit and
their functions individually.
are
considered
Foreman, T K and Deakin, R 'Computer bugs' Lab. Pract. Vol 33 No 8 (August 1984) pp 11-14 An account of one user's experience and problems with an Epson HX20 is given. The portable's user, Foreman, works in the department of orthopaedic and accident surgery of a UK hospital. He highlights the pitfalls that befell him and his coworkers in a project to establish a system for testing volunteers, logging data accurately and being able to access all previous records quickly and easily without wasting the time of the volunteers or the staff involved. The team did not have a satisfactory relationship with the dealer from which the computer was bought; it suffered from not having defined the project precisely enough in its initial stages, ie before trying to put the project into practice; the software supplied was inadequate; and differences between the expected and actual costs were significant. Deakin presents the case for suppliers and for the HX20. She concludes by recommending that, for this particular project, it would have been better to use the HX20 for data logging only and to leave verification and storage operations to a desktop -- nonp o r t a b l e - machine.
Last, l D and Linsdall, D K 'Automatic microprocessor-based receivers for the Decca Navigator system' Radio Electron. Eng. Vo154 No 7/8 (July/August 1984) pp 281289 The Decca Navigator is a continuouswave hyperbolic radio navigation system. Two experimental receivers are described. One is for automatic
vehicle location. [he other is hand portable. Last and Linsdal! first describe conventional receivers and the ambiguities that arise in data obtained from them. The authors then show how such ambiguities can be removed. The system and electronic design of their receivers is illustrated, and the tasks performed by the accompanying software are discussed. A short assessment of receiver performance is made on the basis of 267 h of static operation using off-air signals.
While, M 'Telesoftware - a new educational resource?' Radio Electron. Eng. Vol 54 No 3 (1984) pp 114-116 The feasibility of using broadcast telesoftware in primary education has been studied by the British Broadcasting Corporation (BBC) and the Independent Broadcasting Authority. White traces the history of the project from 1977 to the present. Initially a Phillips Viewdata teletext television receiver was provided with extra page store and buffers and was interfaced to a 32k 8-bit microcomputer at Mullard Laboratories in the UK. Each program was selfcontained and selfdocumenting. Then the BBC adopted for its own use a microcomputer built by Acorn in the UK. Primary schools throughout the UK also bought the so-called BBC model B micro, along with a teletext adapter also supplied by Acorn. Software was developed at Brighton Polytechnic, UK. After three months of test transmissions the BBC Tetesoftware Service was launched in September 1983. White looks at some of the software requirements of the system and how they are being met in its present state of operation. He assesses the value of the project and predicts that telesoftware is here to stay.
F o l l o w i n g up s o m e t h i n g y o u ' v e just seen? Please m e n t i o n Microprocessors and Microsystems
442
microprocessors and microsvstems
Miller, R M 'Plug-in module adds FORTHlanguage and assembler to a handheld computer' Hewlett-Packard J. Vol 35 No 7 (July 1984) pp 37-40 The HP-71 B is a handheld computer from Hewlett-Packard. This issue of Hewlett-Packard Journal is completely given over to describing hardware of and software for the H P-71 B. Programmable in BASIC,the device can be used to control instruments and peripherals, communicate with other computers and operate as an algebraic calculator. Wechsler introduces the HP-71B. She describes the display and keyboard, the file management and file security systems and issues of customization and key redefinition that arose in its design. Customization and expansion procedures are based on an 'open machine' concept, which is explained in the documentation that comes with the HP-71B. Meyers concentrates on the socalled 'soft memory configuration' of the computer. This means that some devices occupying the address space do not have fixed locations -their addresses are assigned to them by the CPU. Meyers shows how this works, and deals with the methods used to extend RAM, to accommodate new RAM plug-ins, and to remove RAM modules nondestructively so that the RAM is ROM like with an independent file chain similar to plug-in ROMs. Configuration of memory-mapped I/O devices, and configuration of everything in daisychain order after addresses have been assigned, are also touched on. The electronics system for the HP-71B is based on seven custom CMOS integrated circuits. Dickies explains how these fit with the rest of the system hardware. He then goes on to describe the bus architecture and operating modes of the CPU. Lindberg deals exclusively with hardware. He presents the H P71B piece bypiece, and includesan account of various plug-in modules and peripherals for use with the device. Blascow and Donnelly have tackled the specific problem of fitting
vol 8 no 8 october 1984
observed data to a mathematical model and finding optimum values for a multivariable function. They used three separate BASICprograms, and based their approach on the Fletcher-Powell method of finding local minima in a function of k variables. Problems with error handling and software testing are summarized. The standard numerical function set of the HP-71B can be extended with the plug-in Math Pac ROM module. Grodd and Patton take a close look at some of the functions of Math Pac, and describe how complex matrix operations, matrix I/O operations, root finding and integration are handled. An algorithm for finding polynomial roots is explained and evaluated. Another plug-in ROM for the HP71B is the FORTH/assembler Pac. The 48 kbyte ROM provides a FORTH kernel, an assembler written in FORTH, an editor written in BASIC and a remote keyboard function. The authors justify the choice of FORTH as an add-on language, and discuss various aspects of the design of the Pac.
Design Adams, l H 'SC84 microcomputer' Electron. Wireless World Vol 90 No 1582 (July 1984) pp 31-34, 64-66 A monochrome VDU circuit for a Z80-based microcomputer is illustrated. The design uses Hitachi VDU controllers with light pen register and interlaced video. It relies on memory mapping and pipelining techniques for its operation and synchronization. Either a monitor or a monochrome television set can be used for display. Adams shows how to connect a monitor to the SC84. Keyboard and parallel I/O interfacing are also discussed. This is the third in a series of articles on the SC84.
The SC84 microcomputer is designed as a series of Eurocards plugged into a common backplane. Adams lists suppliers of frames into which these cards may be fitted. He gives guidelines for setting up a system to meet specific requirements. Also included are notes on connecting various disc drives and on syntax in MCOS, the computer's machine code operating system.
Ewen, G J and Adams, M l 'Microcomputer interfacing: an asynchronous serial communications interface' Lab. Pract. Vol 33 No 9 (September 1984) pp 112-113 An asynchronous serial communications interface has been designed for use with the Apple II and Apple lie microcomputers. The interface can be operated in RS232C or 2 0 m A current loop mode at switch-selectable baud rates. Details of the circuit and the operation of the interface are given. Also included is a 6502 machine code routine which allows the Apple to operate as a terminal in full-duplex mode. A typical RS232C autoloopback configuration is shown.
Penfold, R A 'Parallel to serial converter' Pract. Electron. Vol 20 No 9 (September 1984) pp 17-20 Because RS232C and RS423 ports handle serial data, it is not normally possible to drive directly such things as relays and D/A converters or to read directly switches, A/D converters and similar devices. Penfold has developed a parallel-to-serial converter which allows the use of an RS232C or RS423 port as a parallel port having eight input and eight output lines. The converter is shown first as a block diagram and then as a circuit diagram. The PCB layout of the unit is also given, along with the component arrangement. Details of the construction and operating needs of the device are included.
Adams, J H 'SC84 microcomputer' Electron. Wireless World Vol 90 No 1583 (July 1984) pp 51-53, 63
Williams, J 'Take advantage of thermal effects to solve circuit-design problems'
441
EDN Vol 29 No 13 (28 June 1984) pp 239-248 Instead of trying to eliminate or compensate for thermal parasitics in circuits, designers can use them to solve measurement and control problems. As an example Williams shows how, in a precision temperature controller for a small oven, a resistor switch in series with the thermistor can generate a step input for testing the circuit's response. Another application for temperature control is a thermal RMS/DC converter. Williams proposes a circuit that overcomes the drawbacks associated with the usual conversion process of rectification and averaging. Yet another example is the thermal flowmeter for low fluid flow rates, or for measuring air or gas flow. The final circuit in the article is for a thermally stabilized oscillator.
Applications Ewins, A l 'Micro-controlled cassette recorder - - 2'Electron. Wireless World Vo190 No 1582 (July 1984) pp 61-62, 67 Three sources of error in high~ speed digital multichannel designs for recording serial data from the output of a microcomputer are imperfections in tape quality, dirty tapeheads and indifferent transport of the tape across the head. A technique that is far less sensitive to these sources of error, says Ewins, is frequency shift keying (FSK). He presents circuit diagrams of an FSK modulator and demodulator. Based on Signetics designs, the circuits have been augmented by Ewins to overcome some of the problems associated with the high-frequency pre-emphasis circuitry. Various components in each circuit and
their functions individually.
are
considered
Foreman, T K and Deakin, R 'Computer bugs' Lab. Pract. Vol 33 No 8 (August 1984) pp 11-14 An account of one user's experience and problems with an Epson HX20 is given. The portable's user, Foreman, works in the department of orthopaedic and accident surgery of a UK hospital. He highlights the pitfalls that befell him and his coworkers in a project to establish a system for testing volunteers, logging data accurately and being able to access all previous records quickly and easily without wasting the time of the volunteers or the staff involved. The team did not have a satisfactory relationship with the dealer from which the computer was bought; it suffered from not having defined the project precisely enough in its initial stages, ie before trying to put the project into practice; the software supplied was inadequate; and differences between the expected and actual costs were significant. Deakin presents the case for suppliers and for the HX20. She concludes by recommending that, for this particular project, it would have been better to use the HX20 for data logging only and to leave verification and storage operations to a desktop -- nonp o r t a b l e - machine.
Last, l D and Linsdall, D K 'Automatic microprocessor-based receivers for the Decca Navigator system' Radio Electron. Eng. Vo154 No 7/8 (July/August 1984) pp 281289 The Decca Navigator is a continuouswave hyperbolic radio navigation system. Two experimental receivers are described. One is for automatic
vehicle location. [he other is hand portable. Last and Linsdal! first describe conventional receivers and the ambiguities that arise in data obtained from them. The authors then show how such ambiguities can be removed. The system and electronic design of their receivers is illustrated, and the tasks performed by the accompanying software are discussed. A short assessment of receiver performance is made on the basis of 267 h of static operation using off-air signals.
While, M 'Telesoftware - a new educational resource?' Radio Electron. Eng. Vol 54 No 3 (1984) pp 114-116 The feasibility of using broadcast telesoftware in primary education has been studied by the British Broadcasting Corporation (BBC) and the Independent Broadcasting Authority. White traces the history of the project from 1977 to the present. Initially a Phillips Viewdata teletext television receiver was provided with extra page store and buffers and was interfaced to a 32k 8-bit microcomputer at Mullard Laboratories in the UK. Each program was selfcontained and selfdocumenting. Then the BBC adopted for its own use a microcomputer built by Acorn in the UK. Primary schools throughout the UK also bought the so-called BBC model B micro, along with a teletext adapter also supplied by Acorn. Software was developed at Brighton Polytechnic, UK. After three months of test transmissions the BBC Tetesoftware Service was launched in September 1983. White looks at some of the software requirements of the system and how they are being met in its present state of operation. He assesses the value of the project and predicts that telesoftware is here to stay.
F o l l o w i n g up s o m e t h i n g y o u ' v e just seen? Please m e n t i o n Microprocessors and Microsystems
442
microprocessors and microsvstems