ZB74-bus CPU Board
|PCB Circuits (click to enlarge)||Circuits and Info|
Eagle CAD: 1. CPU, ROM, RAM
Eagle CAD: 2. Memory Address Decode
Eagle CAD: 3. M62-bus Male Edge Bd. Connector
Eagle CAD: 4. Possible PCB Layout
(Bill of Materials)
I simply provide you with information to build your own breadboard computer.
This is a multi-board Z80-based computer that requires a backplane, a CPU board and a UART board as a minimum to communicate via your host PC terminal emulator program like Tera Term v4.1.
We're examining the CPU board here.
As you know, the Z80 as an 8-bit CPU is limited to addressing 64KB of memory. With bank switching, Peter Murray's design permits up to 1MB of memory. Even more can be utilized by a Memory Expansion Board (MEB).
The CPU board contains 512KB ROM and 512KB RAM that is paged through BANK_0 and handled by writes of 0 or 1 to I/O address $00:
- If Bit 0 of I/O address $00 is set to 0 (default) then ROM is chosen for the selected bank.
- If Bit 0 of I/O address $00 is set to 1 then RAM is chosen for the selected bank.
Bits 1 to 5 configure the XA14 to XA18 address lines which select the 32KB page we wish to use.
How much memory does MBC v3 have?
1MB. This does not include a memory expansion board that will be developed at a later date.
I see the schematics. Where is the Bill of Materials parts list?
The BOM is at the bottom of the adjacent panel.
How big is the SBC and what will the printed circuit board look like?
The SBC PCB measures 4" wide x 3" high. Click on the adjacent thumbnail to see a possible parts layout.
Some of you may notice the connector is similar to the RC2014, but the bus layout is not. This layout is new whereas the RC2014 has been adapted several times over the last several years.
Note: M62 Bus is copyrighted by Peter Murray of Murray Electronics, http://www.39k.ca
Tags: Z80 MBC, 1MB memory, bank switching