View Full Version : TRS 80 Color Computer 2 -- Upgrades

3rd July 2010, 14:42
It's Hardware pr0n time !!!!!

Our esteemed Amibay Member fatbob_gb has kindly donated his TRS-80 CoCo2.

It's in fabulous condition and is the Std Color Basic 16K type.

The Coco is quite unique in that its based on the Motorola 6809E CPU which was a brave step for the time... It consists of a Motorola chipset solution, namely the SAM multiplexer, 6821 parallel interface adapter & the good ole MC6847 Video display generator as used on the Acorn Atom too. As well as other support Logic chips.

The 1st upgrade involves replacing the ROM.
All CoCo's shipped with a standard 2364 8K Eprom containing std Color Basic. An etended Basic interpreter was supplied as a plug in 2364 Eprom to co-exist with the already fitted color basic...
This later version of the CoCo 2 was supplied with Color Basic v1.3 which was a modified v1.2 to provide the SAM timing changes required for the higher density RAMS.. It was backwards compatible.

This later revision CoCo 2 has also done away with the 2 x 2364 8K Rom sockets as before, but has a std 28Pin DIL socket.
Now the 2364 is not pin compatible with a 27128 16K Eprom and Tandy provided Jumper locations on the PCB allowing the ROM socket to be re-configured for 2364 at 8K or 27128 at 16K.
This of course means burning a custom Eprom which is made up of 2 8K images.

Extended Basic V1.1 --0h -1FFFh
Color Basic V1.3 -- 2000h - 3FFFh

Ah it's all good fun.... And surprised it worked perfectly first time.. :thumbsup:

The 2nd upgrade is upping the RAM from 16K to 64K
During this period in the 80's DRAM prices fluctuated a lot, so manufacturers built in many options for producing home micros.

This Revision of the CoCo uses 2x 4416 RAMS to provide 16K, notice the white connectors either side of the RAM, this allowed the system to be upgraded using a daughter RAMboard OR replacing the 2 onboard RAMS with 4464 DRAMS & closing one jumper..
In view of this upgrade path, Tandy kindly fitted 2 18pin DIL sockets for the RAM......
xc8 - Chris kindly donated some 4464 RAMS to allow me to carry out this upgrade, many thanks my friend. :thumbsup:

So there you have it, we now have a TRS 80 CoCo II 64K Extended Basic model.....:D

Again Many Thanks to fatbob_gb & xc8 for their extreme kindness in providing the gubbins...

And now the piccies....:cool:

( Time to start repairing some BBC Model B boards now ;) )

3rd July 2010, 17:00
Very nice indeed.

You managed to do more in 4 hours than I had done with it in 23 years.

It is so good to see that it has gone to a good home with someone who can properly appreciate it.

3rd July 2010, 17:36
some nice work there

Extra Ribbits from me for the nice Porn & write up :thumbsup:

11th July 2010, 14:13
nice successful operation!

I am glad that the RAM chips worked and gave a new life to your micro!


11th July 2010, 14:24
It really looks mint! Congrats on the new system TheCorfiot :thumbsup:.

11th July 2010, 18:04
Good work,
Now all you need is NirtOS 9 (free download ) and a floppy drive.
a very interesting "project" is to get the GUI "Multi-Vue" up and running in OS 9.
Multi-vue takes a bit of work, but it is a neat project for the CoCo (I just cant remember if it for CoCo 3 only)
Below are a few pictures of my old set up, I actually had a CoCo 1 set up on the table to the left, the CoCo 2 in the middle and the CoCo 3 with an RGB monitor on the desk. I just had to swap the floppy drive between the 2 units but moving the Cartridge pak.

11th July 2010, 21:16

Nice stuff there! I've got my CoCo but never haven't really even used it. :) The main reason I bought it was because that's what my very first computer was.