ZX81 Hardware

Baffa-2 is an educational project that allows the learning of computer hardware from the 8-bit computer designs widely used in the 1980s.

It started as a CP/M Z80 machine on Grant Searle's "CP/M on breadboard" and also as an emulator I wrote to run the original files (ROM and CP/M) but grew into many other projects

More info about Baffa-2 project.

Features:

CPU: Z80 running at 3.25 MHz.
Storage: Cassette Tapes.
RAM: 1K Byte (original), 2K Bytes (microdigital/microace) or 32K Bytes (modern clones). Expandable to 64KB.
ROM: 4K Bytes (ZX80) and 8K Bytes (ZX81), switched off when CP/M active.
Supports Basic or Forth using a modified ROM.

More info about...

ZX81 PCBs

ZX81 Kit

ZX80/81 Setup

Backplane Bus Pin Assignments for this project

Pin	Signal	Pin	Signal
1	A0	31	D4
2	A1	32	D5
3	A2	33	D6
4	A3	34	D7
5	A4	35	-
6	A5	36	-
7	A6	37	-
8	A7	38	!RESET
9	A8	39	GND
10	A9	40	VCC
11	A10	41	!RFSH
12	A11	42	-
13	A12	43	2CLK
14	A13	44	-
15	A14	45	!HALT
16	A15	46	-
17	-	47	!WAIT
18	VIDEOCLK	48	!NMI
19	!M1	49	-
20	!CLK	50	ROW_CNT_B
21	CPUCLK	51	ROW_CNT_C
22	!INT	52	ROW_CNT_D
23	!MREQ	53	-
24	!WD	54	OLD_SYNC
25	!RD	55	ZX81_MODE
26	!IORQ	56	!KBD
27	D0	57	-
28	D1	58	-
29	D2	59	IC11_PIN4
30	D3	60	IC5_PIN9

Baffa-2 Boards - ZX81 Compatible Computer

This setup implements a Sinclair ZX81 clone on Baffa-2 Homebrew Computer. It's based on Grant Searle's ZX80/81 Project, heavily inspired by Wilco2009's Board (Alejandro Valero) and my own experience after had built it (... and fixed some Zeddies). It uses Z80 CPU and Dual Clock boards from Baffa-2 Basic set and has 32KB RAM, 4K/8K ROM option (ZX80/ZX81) and allows you to use a PS/2 or original keyboard.