6/20/2024 11:00 PM: -- Breadboard CoCo - Part 2: Meet The Chips

The CoCo1 is a simple design. But only if you have a deep understanding of the chips involved.

There are 4 main chips at the core of CoCo1 that implement the basic functionality:

• MC6809E:- Central Processing Unit (CPU)
• MC6883 / SN74LS783:- Synchronous Address Multiplexer (SAM)
• MC6847:- Video Display Generator (VDG)
• 2 x MC6821:- Peripheral Interface Adapter (PIA)

In addition we have the ROM and the RAM. Which were technology common to the early era of 8 bit computers. We'll cover them later, when we get to it.

• 2 x 8k ROM
• 8 x 4k/16k/64k x 1bit DRAM

Then we have the glue logic chips:

• 74LS273:- Octal D-Type Flip-Flop With Clear
• 74LS244:- Octal Buffers and Line Drivers With 3-State Outputs
• 74LS138:- 3 Line to 8 Line Decoder/Demultiplexer
• 74LS02:- Quad 2-Input NOR Gate

These tie the above chips together.

The rest of chips and components in the CoCo are to support the I/O - The bit banger RS232, the cassette port, the joystick ports, the video & sound.

I'll be breadboarding only the above chips minus the DRAM and ROM. I'll use the SRAM and the FPGA fabric in the FPGA development board for those. And I'll have the FPGA do the I/O as well.

Next we'll check the CoCo1 schematics!