The motherboard

A project log for MRC6502 - Modular Retro Computer

MRC6502 is a fantastic opportunity to learn more about digital electronics and 6502 assembly programming... step by step.

padnestpadnest 01/21/2022 at 07:590 Comments

This is essentially the board that houses the other boards (modules) and provides some basic functionalities as system clock, arduino control, power-up reset, etc.

The motherboard has:

NOTE: this is still a prototype... I may have to change something if necessary.

A bus socket is unpopulated (for now) to easily connect the probes.

Schematics: here

Bus connectors (1)

All bus connectors are identical so child boards can be installed in any place.

The bus has the following signals:

Arduino connector (2)

An Arduino MEGA can be connected for developing and debugging purposes:

Power supply (3)

A DC 5v regulated power supply must be use. A 3000mA of max current ouput should be fine. 

Power-up reset (5)

When switched on the 555 timer, configured in Monostable mode, keeps down the reset line for about 750 milliseconds. The same time is guaranteed when the reset button is pressed.

System clock (6)

A 4Mhz oscillator module provides the (fast) system clock.

Arduino can takes the control (A-FOSCEN signal) of system clock generation (A-CLK signal) in order to stepping CPU execution, access to memory or devices, running at slow rate, etc.

Next step: memory mapping.