High speed data modem

devices. Other new prices for plastic packaged versions of F8 peripheral circuits bought in I00 off quantities are: 3861 parallel I/O now £5.13; 3852 dynamic memory interface for £5.88; £5.88 also for the 3853 static memory interface; and £4.69 for the direct memory interface. The two new program storage units increase the memory capacity of the standard 3851 from 1024 to 2048 bytes and also add memory addressing flexibility by including an additional data counter on the chip. Timer functions are provided by an 8-bit binary counter with program-selectable count rates of I, 4, 8, or 32/~s giving up to 1 /.zs timing accuracy or 8 ms time-out. The two devices, 3856 and 3857, use their I/O pins differently. The 3856 contains two bi-directional 8-bit I/O ports like the 3851 plus a strobe output used for handshaking control of peripheral logic. The 3857 has no I/O ports but provides 16 address lines and two control signals to drive external memory. Samples of the two PSUs are now available and price for 100 off plastic encapsulated devices is approximately £12 each. (Fairchild

Camera & Instrument (UK) Ltd., Kingmaker House, New Barnet, Harts EN5 IN)(. Telephone: 01-440 7311)

High speed data modem The first of RacaI-Milgo's new range of high speed data modems featuring microprocessors is the MPS 48. A powerful custom-built microprocessor, specially developed for use in the 4800 bit/s modem, provides faster and more reliable data communications links. The MPS 48 increases operational efficiency in multidrop systems by providing fast equalization. A unique equalization sequence gives an RTS/CTS (request to send/ clear to send) time of 26 ms while operating at the full data rate - half the time required by conventional 4800 bit/s auto-equalized modems. The automatic equalizer continually updates to ensure optimum performance under changing line conditions and can also completely re-equalize on incoming data. Microprocessors are used because the resulting compact design permits

Vol 1 no 3 february 77

a wide range of plug-in options to be accommodated including facilities for both analogue and digital loopback in point-to-point and multidrop systems. Other plug-in options include a low speed secondary channel and dual 2400 bit/s channel operation. The special front loading construction, similar to RacaI-M ilgo's recently introduced 26LSI, allows all printed circuit boards - standard and optional - to be changed within seconds without removing the modem from its rack. 'On-line' compatible

with RacaI-Milgo's 27 LSI modem, it complies with the CCITT recommendation V.27. Measuring only 5 x 8 x 19 inches two modems can be mounted side-by-side in a standard 19 in. rack. The MPS 48 can be operated over unconditional leased two or four wire telephone lines in point-topoint or multidrop polling config~Jrations for 'dial-up' over the public switched telephone network where permitted. (RacaI-Milgo Ltd., Bennet

Road, Reading, Berkshire, R G2 055. Telephone: Reading860233)

TMS 9900 family expanded A lower performance 9900 and four new peripheral circuits have been added to the TMS 9900 microprocessor family by Texas Instruments. Although a 16-bit wide microprocessor, the new TMS 9980 will compete in the medium performance range dominated by the major 8-bit microprocessors from I ntel and Motorola. Fully software compatible with the TMS 9900 and sharing the same I/O system, the 9980 also contains the system clock generator and oscillator on a 40-pin chip. All 9900 instructions including hardware multiply and divide can be executed. The 16-bit address and 8-bit data bus provide compatibility with byteorganized memories. Like the 9900, a simple serial I/O port is included in the CPU chip (the communications register unit - CRU) with the capability for direct memory access, memory mapped I/O and six interrupts including a non-maskable and a reset input. Pricing is not yet given but will prove cost-effective in applications where memory and I/O requirements are small. Samples will be offered from the first quarter of this year. The first of the new peripheral circuits is the 9904. Driven by an external crystal, the 9904 is a low power Schottky 4-phase clock generator for the 9900 and the three other new peripherals. A programmable system interface, usable with both 9900 and 9980 systems, interfaces directly with the processor's CRU port and provides three functions:

interrupt priority allocation; I/O control and interval timing; and up to 15 individually maskable interrupt lines or 16 programmable I/O ports under program control. Designated the 9901, it is packaged in a 40-pin DIP. One of its interrupt lines can optionally be programmed as a wraparound interval timer with resolution ranging from 21 #s to 669 ms. A single TTL level clock and +5 V power supply is required. The third introduction is an NMOS asynchronous communication controller in an 18-pin pack which can use the 9900's or 9980's serial port. The 9902's data rate is program selectable from 5 to 76800 bit/s, with 1,1.5 or 2 stop bits and even or no parity. An interval timer gives resolution from 64 #s to 16 384 ms and a +5 V power supply and TTL level clock is needed. Synchronous communication control is provided by the 9903 which interfaces to the processors in the same way as the 9902. Data rates range from DC to 250kbit/s with a choice of various data transmission protocols. Character length and sync register are programmable and this circuit also includes an interval timer. The 9903 is packaged in a 20-pin pack with a TTL clock and a +5 V power supply needed. Three static RAMs have been added to the NMOS 1 kbyte memory line-up. All are organized as 256 x 4 with a choice of three speeds - 1/~s, 650 and 450 ns maximum access and read/write cycle times. The TMS 4039/2101 is a 22-pin device with separate input and output buses, out-

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