This is a learning project for getting a serial monitor working on a modified Multitech MPF-1 Single Board Computer based on the Z80 microprocessor.
The is a single board computer designed
and build in the early 1980's for computer education. It is a Z80 based board with the traditional 7-segment
display, a small keyboard and monitor in EPROM. The idea is to create simple programs in menonics, assemble it by hand and
enter the program code in hexadecimal format. The monitor supports a simple single step mode and code to inspect
memory and registers.
The goal for this project is, apart from learning Z80 assembly, to extend the development environment with an proper graphical editor, cross-assembler and a facility to transfer code from the host to the target machine. My solution is to add a serial port in hardware and some Hex-intel receiver code on the target system.
The project has several parts:
- Modification of the hardware
- Porting an existing monitor program
- Setting up an cross-assembly environment and temporary upload facility
- Adding hex Intel upload and download code to the monitor
The MPF-1 has a bread-board area which is used to add a Z80-DART integrated circuit. The initial version used the native Z80-CTC as baudrate clock source.
More information on the hardware modification can be found at http://electrickery.nl/comp/mpf1/modifications.html#dart.
An other option is the Serial_MEM_MPF_B board, that has the DART, the monitor ROM and a configurable amount of RAM. The KiCAD files are in the KiCAD directory. The board has a minor flaw, but it is easy to fix (connect U7-18 with U7-20).
More info on the site linked above.
The starting point for the monitor is the monitor from: https://github.com/MatthewWCook/Z80Project/tree/master/Z80%20Monitor%20Part%201/Code. Only some addresses had to be changed and the 16550 UART file replaced by Z80 DART code.
This monitor for a D.I.Y. Z80 system only has three options, ideal for porting and extending afterwards.
Before adding the hex-intel code, I added some features that supplement the MPF-monitor commands to get some feeling for programming Z80 code.
The development system is Linux based and uses the Z80 assembler from https://github.com/udo-munk/z80pack. This is different from the assembler used for the original monitor, but the conversion is simple. The z80pack/z80asm can generate hex-intel directly, making is easy to upload the code with minimal conversions.
A very useful part of the project, certainly for code fragments larger than a few bytes is a temporary upload facility. For this an Arduino based ROM-emulator is used, which allows transferring code to a RAM chip which is part from the Z80 address space. See https://github.com/electrickery/ROM-emulator. This is a comfortable base to extend the monitor with it's own upload functionality.
Basically this does what is required, but limited to the memory area controlled by the emulator. As programming is in C++, writing hex-intel upload code is quite trival. The goal here is to redo this and more in Z80 assembly. An new address offset option was added, as the generated hex intel assumed starting address 2000h, the address of the emulated ROM, but the emulator exposes only the first 800h bytes from its RAM to the target environment. An offset command command compensates for this.
A small Python3 script uploads the hex-intel code to the emulated ROM. It reads the file line for line and sends it over the serial line to the ROM-emulator. As the response is printed too, the process can be monitored.
Usage:
sh ./asm.sh Z80Monitor.asm
python3 'romEmuFeed.py' 'Z80Monitor.hex' 2000
The second argument of the script compensates for the target address in the hex intel file with respect to the address in the RAM.
Startup banner and help:
Changes made to the dump command:
A planned change is to add a download of hex-intel via the monitor too, making a comparison on the host possible.
fjkraan@electrickery.nl, 20220216