RADAR PRINTER INTERFACE
Technical details

Sub-unit Description

Input Interface PCB
This was a small circuit board in the unit that provided both opto-coupled current loop and TTL data input interfacing to the Microprocessor PCB. Either current being passed through the current loop input or a TTL low input provided a high (mark) to the Microprocessor.

Microprocessor PCB
This Z-80 based microprocessor card ( the MCB 80) received input data from the Input Interface PCB. It was imported from USA where it was manufactured by Space-Time Productions and marketed by R.W. Electronics of Chicago, Illinois.
The Z80 Microprocessor CPU was run at 2.5MHz clock speed so that the necessary clock rates for the 50 baud input and 1200 baud output functions could be developed.
An 8255 Programmable Peripheral Interface (PPI) provided the output for the parallel printer and a Z80SIO dual async/sync serial I/O chip provided the 50 baud Baudot serial input and 1200 baud ASCII serial output.
Though the board had space for three 2732 eproms only two were fitted and they contained the dedicated code for the particular radar station. This was necessary as each was compiled with its own station height for the wind calculations. The board's memory was made up from four 2114 (1024x4bit) static ram IC's.

The Program

The Fortran Program to calculate winds for WF44 or WF3 radar was written by A.L. West in 1983.
The program checked the input data for validity, calculated the wind data and then output the raw data to both the serial and the parallel outputs connectors and also sent the calculated data to the parallel output.

The original fortran program had been designed for an output that would fit on 40 column printer. (This is achieved by suppressing the Time and Elevation hundreds from printing.) This program formed the basis of the code used in the Radar Printer Interface with its associated cheap dot matrix 80 column printer. For each station where this unit was used, the program would be recompiled as the specific Station height and name had to be included in the source code.

Input Data Format

The input data from the parent radar was of the following form:-
50 baud, 5 data bits, 1 1/2 stop bits either as 40mA current loop or TTL data

Output Data Formats

The output data was in two forms:-

Parallel output
8 bit parallel data with negative going strobe pulses

Serial output
1200 baud, 8 bit, no parity, 1 stop bit, ASCII data

Fault Analysis
For fault analysis an eprom was fitted that had been programmed wth monitor routine. It communicated with an external terminal at 300 baud.

References
(1) Equipment handbook EH643