M62-bus System Buses Monitor Board

Eagle CAD: 1. System Bus Monitors

Eagle CAD: 2. CPU Single-Step

Eagle CAD: 3. M62-Bus Male Bd. Edge Connector

Eagle CAD: 4. A Possible PCB Layout

BOM

(Bill of Materials)

PLEASE NOTE: I do not sell production boards. If you would like to buy an M62 Z80 system board/parts kit, contact Peter Murray, Peter@39k.ca

I simply provide you with information to build your own breadboard computer.

Overview

The M62 Bus Monitor board can be used with either the SBC or SBC2 which are M62-bus based, but not the ZB64PC-bus SBC.

Operation

There are 6 MC14495 chips that convert 4 binary signals to their hex equivalent. As an example, hex value F we know to be 1111 in binary. By hooking up 4 of them to the 4-bit groupings that make up the 16-bit address bus, we can monitor the current values on said bus. The same is true for the 8-bit data bus but we'll only need 2 chips.

The LEDs are common cathode units as you guessed because their common feeds on pins 3 and 8 are connected to ground.

The Control Bus uses a '245 driver to connect all of the Z80 control signals to LEDs without loading down the current-load sensitive Z80 bus.

The CPU Single-Step circuitry uses a 555 timer to fire the NAND latch, IC9, sequentially without keybounce from the STEP switch, S1.

When M1 fires with each new instruction, pressing the STEP button fires the WAIT input signal to the Z80. While waiting, it simply runs NOPs. Please keep in mind that you may only see the beginning of each new instruction, its first operand, due to the way WAIT works. If you need more, consider an ICE.

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 SysBusesMonBd and what will the printed circuit board look like?

The PCB measures 100mm x 100mm (4" x 4"). Click the adjacent thumbnail to see a possible parts layout.

Note: M62 Bus is copyrighted by Peter Murray of Murray Electronics, http://www.39k.ca