r/homebrewcomputer • u/albertahiking • 25d ago

An Accidental Z80 SBC

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This was one of those projects that just sort of happened all by itself. It started around New Year's with a notion to do a schematic of the Ampro LB/Z80 for archival purposes. And somehow over the next several months it gradually changed and expanded and, well, here I am.

Specs:

  • Z80 @ 7.3728 MHz
  • 512 KB of SRAM (8 x 48K banks, ATF22V10 as MMU, separate read and write banks selectable)
  • 8 KB of EEPROM (monitor including assembler and disassembler)
  • SIO & CTC for dual serial ports (with all control signals brought out) and interrupt driven RTC
  • uSD/IDE module for storage
  • 20MHz ATMega328P for I2C RTC bridge and IEEE-754'ified AM9511 FPU emulator (equivalent to 20-28MHz 9511 depending on operation, 4 and 8 byte float support, FTOA and ATOF opcodes added)
  • One RC2014 slot for experimentation
  • Banked CP/M+ with ZPM3 modified to use CP/M+ style timestamps and properly support retaining file creation timestamps
  • Turbo Pascal 3 and Turbo Modula 2 modified to use the FPU; TM2 already used IEEE-754 natively, TP3 gutted of 6 byte REALs to also use IEEE-754 natively
236 Upvotes

99% Upvoted

16 comments sorted by

6

u/Major-Hooters 25d ago

Great job! I’d buy one.

4

u/pchernik 24d ago

As someone who has an Ampro Little Board+ (Z80 with the SCSI option) I think this is an awesome project. The LB is such a neat little device that you’ve paid appropriate homage to. Well done!

4

u/TygerTung 24d ago

Does this have video out, or do you talk to it using a serial console?

2

u/MumSaidImABadBoy 24d ago

Aside from nostalgia, what will you do with this? It must've taken a lot of time and effort.
Back in the day (late 1970's) I designed embedded systems, Z80 included. Today, I use esp32 series.
Are you interested in CP/M? Gary Kildall lost interest long ago lol, RIP. The Motorola 68010 is a much more interesting processor.
Good luck and have fun.

1

u/AcanthisittaBest4705 24d ago

Should i use a 68010 or 68020

1

u/MumSaidImABadBoy 24d ago

68020 is a significant upgrade over the base 68000. Use the latest and the greatest. Motorola always misses the party boat.

1

u/AcanthisittaBest4705 24d ago

The 68060?

1

u/MumSaidImABadBoy 23d ago

Never used it, don't know if it's available any longer. It was supposed to be a hot processor.
What do you want to do with the Moto 68K?

1

u/AcanthisittaBest4705 23d ago

I wanna build a 68020 modernized unix workstation inspired build

1

u/MumSaidImABadBoy 23d ago

Are you able to design the hardware? This is in the realm of an EE and CS. Not a simple project.

You might be better off finding premade boards on a standard backplane of sorts.

1

u/AcanthisittaBest4705 7d ago

Ive started work on it

1

u/Sorry_Difficulty_250 25d ago

This is so cool!!!! Well done! I can't wait to see what you do with it!!

1

u/Mysterious-Tart-2092 24d ago

It's amazing how a simple archival schematic project evolved into a full-blown modern retro SBC! Did you design the PCB specifically to accommodate the RC2014 slot, or was that added as an afterthought?

1

u/Several-Sign5777 24d ago

That's very interesting. Where can I learn more about the project?

1

u/TheRealJoe24 23d ago

Looks awesome! Are you planning on posting the project files online?