This is to announce that I have now added a "do-it-yourself" section to
my website at http://www.nouspikel.com/ti99/titechpages.htm
You will find a do-it-yourself primer, a guide on how to open the
console, a summary of TTL pinouts, and several pages dealing with the
Some of which you may have already seen:
- Installing a second RS232 card.
- Powering the joystick port and/or building a PC joystick adapter.
- Replacing ROMs with EEPROMs, both in a card and in the console.
- Installing Jeff Brown's interrupt mod.
But I recently added two new pages:
- One deals with a modification to the Widget that makes the 3
cartridges available at the same time, under different GROM bases. I got
this idea from someone in the TI99/4A online user group, but now I can't
remember who (announce yourself for credits).
Here the trick was to design a circuit that would remember wich GROM
base was used last, so it can select the proper cartridge ROMs...
The URL for this one is www.nouspikel.com/ti99/widget.htm
- The other page deals with overclocking the console. Usually this is
done by changing the crystal, or installing a switch to toggle between
crystals. But I wanted to be able to switch speed via software.
So I replaced the crystal with two 3-state oscillators, whose
output-enable pins are controlled via the CRU. Works like a charm: by
simply toggling one CRU bit, I can switch between 3 and 4 MHz and the
TMS9900 doesn't miss a beat (nor a bit).
The URL is www.nouspikel.com/ti99/clockup.htm
I hope you guys find these pages usefull. Have fun hacking your