The RS PA board is a complete computer system on a single Eurocard. it is based on the 4MHz Z80A microprocessor.and it runs CP/M Plus, the latest version of the CP/M operating system. The only extras you need are disc drives, a terminal and a power supply. The board also has a complete STEbus interface enabling memory and extra I/O to be added, so that the system can be expanded to a powerful industrial control system or a scientific computer with a vast range of CP/M software. CP/M Plus and suitable 31/2" and 51/4" disc drives are available separately (see the current RS catalogue). Note that it is not possible to make CP/M run on any arbitrary disc drive: the drive characteristics must be incorporated both in CP/M itself (in the BIOS, the hardware specific part of CP/M) and in the "boot" EPROM that the RS PA uses on power-up to load CP/M from disc. For this reason, only drives compatible with RS drives are supported. Of particular importance are the step rate, number of tracks and disc size.

There is a great deal of electronics on the RS PA board. The Z80A runs at 4 MHz, and can access the 64K of fast dynamic RAM with no wait states. An EPROM of up to 32K,can be switched in and out of the memory map under software control, and bank-switch bits can be used to access up to 192K of extra memory via the STE bus interface.

There are several I/O devices on board. Serial communications are handled by a Zilog SCC Serial Communications Controller and RS232 buffers. One channel is normally used by the system console device,for example a Video Display Terminal (VDT or VDU),and the other channel is configured as the system list device, for use with a serial printer. The baud rates on both channels can be set by a CP/M utility program and the standard boot EPROM contains a program for automatically finding the baud rate of the system console device and running at that speed. There is also a parallel latched input port which can be used by a parallel keyboard, although this is not supported in the standard BIOS. For modification details consult the RS CP/M Plus User Manual Supplied with the CP/M Plus software.
The disc controller is an advanced single-chip design that will control double density, double-sided disc drives with 80 tracks per side (RS FD35F or RS FD55F).

The STE bus interface allows the RS PA to act as the default bus master. Because the STE bus is multiprocessing, up to three masters can use the bus. This means that up to two potential masters may be added. The RS PB boards may be configured as potential bus masters.

There is a large range of I/O boards for the STE bus. Consult the current RS catalogue for details of analogue and digital I/O, memory expansion, EPROM programmers and STE hardware.

Complete withManual reference 631-862

Manufacturer: RS Components
Date: March 1986

This exhibit has a reference ID of CH16777. Please quote this reference ID in any communication with the Centre for Computing History.

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