Well, I’ve had a frustrating weekend! The EEPROM programmer which I bought from China turned out to be a load of rubbish, so I’ve sent it back and I’m building my own EEPROM programmer with an Arduino Uno.
I’m also taking the opportunity of the time it’ll take to get that working to get some new kit in. I’m still sticking with the Z80 for the time being, I don’t want the additional trouble of wiring in the 6809 for the time being. So, here’s the component list at the moment:
Zilog Z80: Our CPU. Zilog 8470 Dual UART: For serial communications. The Z80.eu page has a great article on the Amstrad PCW's serial and parallel interface, which happens to also give some examples of interfacing the Z80 to the D-UART/DART. TI MAX232: An RS-232 interface. 128K Parallel Flash RAM: This takes the place of EEPROM, and is easier to program, not needing a 12V power line. I'll only be using the lower 16Kb. 32K RAM: For the time being, in 8K chips. Some JK Flip Flops, LEDS, and a switch: For basic test IO purposes.
And here’s the test OS which will go on the Flash RAM once the programmer is working. This basically waits for the switch to be pressed and then changes the LEDs by adding 1 to the binary value which they represent in 8 bits:
CPU Z80 ORG 0000H
PORT0: EQU 0H PORT1: EQU 1H
START: NOP CHECKFORKEYDOWN: IN A,(PORT0) CP 1 JP NZ,CHECKFORKEYDOWN CHECKFORKEYUP: IN A,(PORT0) CP 0 JP NZ,CHECKFORKEYUP OUTPUTNEXTNUMBER: INC B LD C,PORT1 OUT (C),B JP START