MOS 6529 SPI full equivalent - soldering kit

This item is a full replacement for the MOS Technology 6529 Single Port Interface used in the Commodore 16, 116 and Plus/4, where it is used to implement the keyboard functionality and the user port.

The soldering kit offered here allows you to build a fullly compatible replacement for the MOS 6529 SPI based on standard 74xx chips. The PCB is suitable for the both the 74xx652 and 74xx654. Currently, I will ship it with the 74xx654. A 74xx02 is used on the PCB to generate the control signals for the 74xx654.

Allthough I am generally opposed to evil SMD technology, because there is not a lot of space inside the Commodore 116 and Plus/4 I have felt a need to use some SMD components in order to keep the size limited. Still, this is not the worst SMD in the world, it can quite easily be soldered with tweezers and a normal soldering iron. If you can solder mini-DIN connectors in order to build tape and joystick cables for your C16 or Plus/4, you will also be able to solder this adapter.

The MOS 6529 is simple in functionality and you can find many simple schematics how to replace it with standard parts. Unfortunately there is a lot of misinformation and many will produce a non-working or not completely functional 6529B.

Some of the various advices on the internet to build replacements are based on these chips:

• 74xx245 - This is completely wrong and won't work at all, the 6529 is an I/O expander and not a bus transceiver
• 74xx639 - Completely wrong for the same reason: The 6529 is not a bus tranceiver
• 74xx377 - A better idea, as it implements the register needed to retain the written value and combined with open collector buffers, you could use it to repair a C16. However, as the 6529B is a bi-directional I/O expander, this would completely ignore the ability to read from the bus, which makes it not 100% compatible for the keyboard and  completely unusable for the Plus/4 user port.
• 74xx573 - Same comments for the 74xx377 applies, but also transfers bus switching noises during write cycles to the output port
• 74xx574 - Same comments for the 74xx377 apply
• 74xx647 - Actually a really good idea, and gets you quite close. Unfortunately, there is one little catch: The 74LS647 stops driving the output port if you reverse the direction in order to read from the port. With the Plus/4 user port, this means you are actually transmitting data to the device connected to the user port if you read from the port.

But, there exists a 7400 series chip that does allow you to build a fully compatible replacement: The 74xx654. And, if you implement the open collector behaviour with external components, the 74xx652 can also be used and this is what this replacement is using.

You will receive:

• 1 * adapter PCB
• 2 * 10 pin header, round pins
• 1 * 24 pin IC socket
• 1 * 74xx654 chip
• 1 * 74xx02 chip
• 8 * resistor >= 6.8 kΩ <=10kΩ
• 8 * resistor <= 1Ω
• 1 * capacitor 0.1uF
• 1 * Instruction manual

Compatible with:

• Commodore 16
• Commodore 116
• Commodore Plus/4

P.S. should you have a Commodore 116, please attempt to replace it with an original IC, these machines are so rare that they deserve to be as original as possible.