Adding SD2IEC to the Commodore Plus/4

In a recent series on YouTube, I did battle with a Commodore Plus/4 computer from 1985.

It was bought "untested" from eBay, and we all know what that means.

List of things I did:

Modified the power socket to take the more-available Commodore 64 power supply.

Replaced the 8507 microprocessor with a 6502 replacement PCB

Removed the faulty 8591 UART (I didn't need it, I *think it's primary use is to run the 1551 disc drive)

Finally having got the damn thing working, I needed an easy way to load programs. 

I liked the idea of an internally fitted SD2IEC solution, as it's easily available, and as it's compatible with the 1541 disc drive, it should work OK (although no quicker than a 1541!)

You can get the module for about £24 (at the time of writing) fromt The Future Was 8 Bit here.

Inspired by the Tynemouth Blog, where they fitted an SD2IEC to a C16 (here) I proceeded to look around inside the Plus 4's case for somewhere suitable to mount the PCB.

There's not a lot of space inside the Plus 4's case, but I think I could squeeze the board, on a suitable adaptor inside the cartridge port. Sadly this will sacrifice the cartridge port, but I don't have any carts, and it's easily reversible. It also has the advantage that I don't need to cut a slot in the case to facilitate removal of the card.

A minimum of 5 connections are required to make the drive work. 

Pin 22  +5V
Pin 23  IEC CLK

Pin 24  GND

Pin 10  IEC DATA

Pin 11  IEC ATTN

I soldered the required 5 wires onto the board, and fitted the board into the bracket I'd 3D printed.

3D printer files are here

The bracket is a simple thing, with a chamfer on the bottom edge to facilitate clearing the existing cartridge port connector.

The SD2IEC is taped to the bracket with some 'Koptan' tape, to secure it, and provide insulation from the top shield of the cartridge port.

The adaptor & PCB is the slid into the cartridge port. It's a snug fit. 

Once that's fitted, it's over to the wiring.

We can see the required data, clock and atn lines all make there way to U7.

It's easy just to connect the lines from the SD2IEC straight to U7.

The 5V and GND can be picked up from suitable points on the PCB.

Reassemble the machine, grab yourself some software, and enjoy!

There's a whole set of videos on my Plus/4 adventure: