In this project, an old IBM point-of-sale (POS) display is reverse engineered to display arbitrary text. The goal of this project is not entirely clear.
The display in question contains two rows of 20 characters each. The characters on the display are of the VFD type, in blue/cyan.
The electrical interface to the display consists of 4 wires, possibly:
- data A (inverting), D-
- data B (non-inverting), D+
- power (12V) - red
This is most likely an RS485 interface, because there is a 75176 (differential bus transceiver) inside the display.
A very simple RS232-to-RS485 conversion can be done by simply biasing the inverting data pin (data A) to half the supply voltage, and connecting the RS232 data line directly to the non-inverting data pin (data B).
- Figure out baud rate
- Write software to control the display
Possible protocol descriptions:
- possible protocol description: SurePOS 500 Device Commands: 2x20 Customer Display
- appendix G ("Input/Output device commands", page 56) of SurePOS 500 Model XX3 Technical System Reference, version 1.3