Radar Printer Driver Technical

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Technical details

General Description

The Radar Printer Driver was a dedicated Z80 based microprocessor developed from the Alfatron A3000 Communications Interface. It comprised a switch mode power supply, a A3000 modular interface card (the main CPU card), an A3010 serial interface card, and an A3040 Bi-directional Centronics interface.

It was functionally two I/O ports communicating with a CPU with rom and scratch ram. The data input to the serial interface was 5 bit baudot code provided by the radar. This was passed to the Z80 based microprocessor card. The processor checked the data for correct format, calculated the wind data and then sent the calculated data to the centronics interface for output to a parallel printer.

Because the A3000 came with an array of leds on the front panel some better indication of the working condition of t he unit was able to be programmed into its operation. A 'Printer Busy' led flashed for every printer strobe sent out of the centronics interface and also indicated printer busy or off line by being continuously lit. A 'Rx Active' indicated the unit was actively receiving incoming radar data.

Sub-Unit Description

Modular Interface A3000
This Z80 microprocessor based card had 8k of eprom and 2k of ram, as well as 256k of bank switched ram. It was connected to a number of I/O mapped LEDs and switches. It had two Z80 I/O Bus extension connectors with some decoded I/O mapping for external peripheral cards. Two different CPU clock speeds of 4.3 Mhz and 3.07 Mhz were used.
A watchdog reset timer modification was fitted by the Bureau to provided a CPU Reset if no IORQ signal occured for more than one second, this meant if the unit should lockup it would automatically reset. Over all the years of use, there was no evidence that this circuit was being activated - which is an indication of how reliable the unit was.

Serial Interface A3010
The Serial Interface provided one serial RS232C channel of I/O interface for the microprocessor card. It consisted of a 8251 Programmable Communication Interface with a 8253 Programmable Interval Timer which provided the programmable baud rate generation.

Centronics Interface A3040
The Centronics Interface provided the parallel bi-directional I/O channel to the microprocessor card. This card had a 8255 Programmable Peripheral Interface configured for a centronics type I/O on port B and using Ports A and C for handshake and control logic.

Input Interface
The Input Interface was mounted externally to the Radar Printer Driver chassis, in-line with the input data sent from the radar. This circuit provided the opto-coupled current loop data input interfacing for the Serial Interface.