I/O interface board
Many thanks to Nigel Goodwin for his help in this project, and comp.sys.psion users for IOW commands.
This works with any device with a RS232 serial port.
Sorry for fuzzy picture. :-)
It's a PIC16C84 based 11 line I/O board. 10 of the lines can be programmed to be either Input or Output.The other line (A4) is an open collector type.
It's based on the PICEX from Dontronics. The PIC code can be found here. Many thanks to the author.
The circuit consists of a 7805 voltage regulator, a MAX232 serial voltage converter and the PIC16C84 with a 4MHZ crystal. Onboard power is supplied via a PP3 9V battery. Only 3 wires are required to connect to the serial port, TX/RX and GND. All input/output voltages are TTL, e.g. 5V.
Software control is via a 6 byte command sent to the serial port. The PIC processes this data and then sets or reads the appropriate lines and sends a confirmation signal back.
If any body wants any OPL code, i'd be happy to help out. :-)
IC1 7805 Voltage converter
IC2 Maxim MAX232CPE
C1 100uF electrolytic
C2 10uF electrolytic
C3 100pF ceramic
C4-C7 10uF electrolytic
C8-C9 10pF ceramic
XT1 4Mhz Crystal
If you want to use the board on any other device than a Psion, swap the RX and TX lines on the 9 pin serial port plug.