I've been kicking around the idea of building a single-board computer around the Zilog Z180 for a while. It fits nicely between my Herring 6502 and Mackerel 68000 projects. It's got the simplicity of an 8-bit processor with a few more bells and whistles...
So a lot has changed since my last update on here, I've redone the address decoding to use a 74138 3-8 line decoder to allow me to partition the address space. I've added some status LEDs to help show the state the computer is sitting in, so I don't...
Address decoding for the m68k is a bit more involved than for most (all?) of the 8-bit CPUs that were around at the same time, and so requires a bit more careful design. The specific things that make it complicated are:The larger (16MB) address spaceThe...
[Path_To_RetroAssembler]/retroassembler.exe -d cegmon.bin cegmonDis.asm The SD Card uses the following FPGA resources: The overall resources show 98% of the logic is used. It might be worthwhile to free up some of the logic elements so it's not...
I've loved the (on-line GodBolt) Compiler Explorer project for a while now. It lets you type code in one window and see it compiled to assembly language in another window. There's a Compiler Explorer site which does 68k cross...
One of the things that's become an increasing problem on this project is the MC68901 Multi Function Peripheral. Way back when I started this project (actually when I ordered the very first MC68010 for it!) I ordered a 68901, almost on a whim, as...
Overview The Nomad board is a 68000/68010 compatible microcomputer with 128K of SRAM and 128K of EEPROM memory, with the EEPROM being in a convenient PLCC socket for repeated removal. The Nomad board includes a MK68901 peripheral chip to...
MOTIVATION After having worked several months on the first Kobold CPU , I got the feeling that it was going in the wrong direction. I was working on a Javascript assembler, and got tangled up in the microcode complexity. I also didn't like that...
I'm about to start assembling the first revision of the Motorola 68000 motherboard. This revision, rev1 (I start my revisions at rev0), includes a few fixes for minor problems in the prototype. None of these problems were show-stoppers, and I was able...
The board is now fully assembled:Notice the adapter I had to make to correct my design mistake with the RAM address bus. Apart from that It's very satisfying to see the finished board, as this is my first real PCB design.But does it actually work?To...
I was going to open up my NEO unit to see what's inside. But, fortunately, people have already done that. There is a CR2032 coin-cell inside that serves as backup to retain SRAM while the AA batteries are removed. Some power users have opened their units...
CP/M is a well known operating system in 1970's and 1980's. It was designed for many different processor family, e.g., Z80, 808x, 68000 and others. Running CP/M is the end goal for many of the processors prototyped with G8PP because that...
The minimal 68030 computer has 512K of RAM and a simple serial port. Here is the memory map of stage 2 68030 computer:RAM 0x0-0x7FFFFSerial port transmit/receive: 0xFFFFF000Serial port status 0xFFFFF001 Bit 0 is TxEmpty, transmit buffer empty...
[Edit: I've added a schematic for this circuit at the bottom of the log!] I'm not sure what exactly I was thinking of when I wrote the previous log about handing the /BOOT line, but it's completely and utterly wrong. Luckily, I realised this when actually...
I hadn't looked on to it for years (no time, creating an extra room in the attic and so on), but it kept itching... On the other hand it seems so strange fiddling around with old hardware, a simple ESP32 has more capabilities and speed than a 68k will...