A telephone interface for HP-IL controllers

of the local area network installed compared'somewhat unfavourably with those of other networks recently introduced, the cost benefits and the ability to link industrial programmable controllers with computer stations were more significant. As emerging local area network standards become adopted by a range of computer manufacturers it is expected that the necessary communications software will also be provided by the makers rather than having to be written by the user.

Morris, D E, Ridolfo, A S and Morris, D L 'A portable computer for field, office, or bench applications' Hewlett-PackardJ. Vol 34 No 6 (June 1983) p 3 Snell, S and Spreadbury, B G 'A telephone interface for HP-IL controllers' Hewlett-Packard J. Vol 34 No 6 (June 1983) p 5

York, D C 'HP-IL and the HP-75 portable computer' Hewlett-Packard J. Vol 34 No 6 (June 1983) p 8

Brooke, E, Livengood, R J, Smith, R C and Myers, T F 'High-capability electronics systems for a compact, battery-operated computer' Hewlett-Packard J. Vol 34 No6 (June 1983) p 10

Hoecker, K R, Schwartz, J R, Young, F A and Johnson, D R 'Handpulled magnetic card, mass storage system for a portable computer' Hewlett-PackardJ. Vol 34 No6 (June 1983) p 15 Patton, D B 'The HP-75 production card recorder' Hewlett-PackardJ. Vol 34 No 6 (June 1983) p 20

Arnold, T J and Thayer, B E 'Integration of the HP-75's handpulled card reader electronics in CMOS' Hewlett-PackardJ. Vol 34 No 6 (June 1983) p 24 The HP-75 portable computer has been designed by Hewlett-Packard for field, office or bench applications. Morris et aL discuss the development of the HP-75 and list its features, eg touchtype keyboard, integral BASIC language system, liquid-crystal display

vol 7 no 7 sept 1983

and 16 kbytes of nonvolatile user memory. The firmware design and file system are also treated. The HP-75 has a built-in HP-IL (interface loop) interface for connection to HP-IL-compatible peripherals and instruments. Snell and Spreadbury explain the electronics operation of the HP 82162A telephone interface developed by Hewlett-Packard for HP-I L controllers. York argues that HP 82162A interfacing is better than RS232C/V24 and H P-I B (I EEE-488) interfaces for use with the HP-75, especially as it can link the HP-75 to the user's large factory computer. The HP-75 portable computer combines the processing capability of the HP-85 personal computer with the CMOS technology of the HP-41 handhold computer. Brooks et al. discuss the individual elements in the system: power supply, timer, display, keyboard, magnetic card reader, HP-IL, clock system, and memory organization. The handpulled magnetic card can store 1.3 kbytes of user data or programs per card. Hoecker et al. give an account of its design and operation, including error handling and extensions. The choice of CMOS technology to implement the HP-75's internal functions was based on the portable battery-operated nature of the computer and the need for large storage space. Arnold and Thayer designed and laid out the digital and analogue circuit parts of the handpulled card reader IC independently and then merged them in a single IC. The designers reduced 1/f noise (ie noise generated by surface states or impurities in the surface of the silicon under the gate of a transistor) by using p-channel transistors for the differential stage inputs. High-frequency instabilities and other problems were solved similarly by careful design considerations. Although there is some overlap in content between these seven papers, each provides details about particular aspects or features of the HP-75 not found in the others and the whole set is a useful guide to the design and operation of the computer.

Stockton, J S 'Growth of processor family boosts

system options' Comput. Des. Vol 22 No 2 (February 1983) pp 71-80 The MC68000 family of microprocessors has been extended to include other processor and peripheral chips, with a view to more applications. For example, the MC68008 is compatible with the MC68000. The MC68008 works with an external 8-bit data bus and reduced address space. The MC68MC68010 virtual machine has the advantage that it recovers control after memory faults. The 32-bit wide data bus on the forthcoming MC68020 allows programs written on the MC68000 to run between two and four times faster. Peripheral support chips included in the 68000 family are the MC68451 memory management unit, the MS68452 bus arbitration module and the MC68450 direct memory access controller. These directly influence hardware and software design. The MC68120 intelligent peripheral controller brings I/O processor capability to the MC68000 family. It supports a local address/data bus that connects the system to peripherals such as disc controllers or communications interfaces. For designers who want a more flexible approach to peripheral support, the MC68901 multifunction peripheral is a combination of miscellaneous interface devices commonly found in small systems. The MC68562 is a two-channel universal communications controller. It supports commonly used asynchronous and synchronous protocols. The MC68590 local area network controller for Ethernet supports the blue-book definition of the Ethernet standard, and both transmission and access mechanisms. It handles the carrier sense multiple access/collision detection serial bus arbitration, by using an algorithm incorporating listen before talking, listen while talking, and retransmit on collision after a random wait. Addresses and data are multiplexed (to conserve pins), and the interface is housed in a 48-pin package. The intelligent multiple disc controller (IMDC) is intended for use with Winchester drives. Both hard and floppy discs can be controlled simultaneously. Data/clock separation

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