Added a UART to the Z80

I added a UART to the Z80 board. The original thought was to use a PIC on a separate board to do the UART function but the PIC wasn't quite fast enough. I ended up using a TL16C550 from Texas Instruments and along with a Microchip MCP2200 UART to USB chip. I've used the MCP2200 many times before as finding a 9 pin RS232 COM port on a PC is getting hard these days. I've been able to get UART input and output at 115.2KBaud with no issues.

Z80 CPU with UART Schematic

Programmer Version 2 now in a box

I made a modification to the programmer board and finally got around to building and testing it. All I did was add a 128Kx8 SPI EPROM for program storage. The original programmer worked fine but the Z80 board, since it has no ROM, had to have a program loaded each time it was turned on. With the EPROM on board, depending on the configuration switches, the Z80 will start up as before (Manual mode), or automatically load a RAM image and start running. There is a second switch to indicate which of the 2 images to load. I also ended up putting it into a box with a 5V power supply to make it a bit easier to work with when away from the lab. The Z80 board is mounted on top with the programmer mounted inside.

The box used was from a different project so that is why the location of the AC input is not exactly where I would like it. The front panel switches are as I described. The top has the reset button along with the programmer status LED. Not pictured is the USB connector (on the left side) for the serial port to the PIC on the programmer to communicate with the programmer software.

The programmer software was also modified to allow programming the EPROM or the Z80.

Programmer Version B Schematic