Commodore 16 internal memory expansion

[yoyodyne]

Hi everyone!

I was repairing a C64 with a bad memory chip this weekend, and
had to sort through all my bins until I found the right one. I sorted
a bunch of others out, and looked up some of their datasheets.
That started me thinking what some of them could be used for, and
I checked out the schematics on the C16. I had the chips I needed
to replace the existing 16k x 4 with 64k x 4 dram.

The C16 uses 2 multiplexers for the address decoding, and I wasn't sure
how to add this memory. I looked on the web, and later did
find a description on adding memory to a C116 that would have
helped, but at first only found a site (commodore16.org) that
sells an external memory expansion.

I then compared the schematic for a Plus/4, and saw that it
uses the exact same multiplexer address decoding, and saw what
I needed to do, just remove 1 pin from the board on each
multiplexer chip, and add the corresponding address line.

Now my C16 has 60671 bytes free!

Here's the exact procedure:

1: remove U5 and U6 (TMS4416 16kx4 dram) and replace with
64kx4 dram (LH2464 in my case). No pins change.

2: pull pin 2 on U7, and run a line from it to pin 7 (A15 line) on U16 (PLA)

3: pull pin 14 on U8, and run a line from it to pin 26 (A14 line) on U16.

Thats it, you now have 64k! Pins 2 and 14 previously were pulled
high with +5v, they were not used on the C16 for internal ram.
I will add some switches to my wiring lines so I can return the C16
to its normal state if need be. Also, A14 and A15 are available at
many places on the motherboard, they don't have to go to the PLA
chip.

I wrote a small Basic program, and tested the Tutorial cart, and
both worked ok, but thats not very extensive testing.

Anyway, it was a fun little project. I spent a couple of hours
researching the web and checking schematics, but it only took
a 1/2 hour or so to make the changes to the board.

Hope this helps somebody!

Brian

[TheRealAnubis]

I know this is an old post, but this is excellent! From other online sources, I have found the jumper wires going to other places, so it's nice to have a choice!

Are you planning to post any pix of your mod?

I've been wanting to make a 64K RAM cart for the C-16, but have been unable to find a schematic for one - any ideas?


Thanks!

[icbrkr]

Old topic is old, but I stumbled across it.

I changed mine to 64K here:

https://www.facebook.com/media/set/?set ... a925c05215

You can see what NOT to do to upgrade as well...

[majikeyric]

I plan to make the mod to my C16s also.

Here a good tutorial : http://www.amibay.com/showthread.php?32 ... AM-Upgrade