TI-99/4A Sideport 32k Memory Expansion
A 32k memory expansion for the sideport of the TI-99/4a
With the abundance of cartridge conversions of EA5 games, that in practice just load the game from ROM space into the 32k expansion RAM, I felt the need to make a consumer oriented 32k expansion. I started this back in July 2016.
The discussion thread took place here on Atariage
I don’t make these anymore, but others do. It is generally available for sale through ArcadeShopper.com
This is intended to be an open-source design, although the schematic and pcb layout were performed with a commercial/proprietary application called Copper Connection. The gerbers are also available for anyone to use for production.
Assembling your own
Look here for a video illustrating how to assemble if you are building your own:
What it is
Functionally equivalent to TI’s 32k expansion ram. It plugs into the sideport of the TI with an edge card connector. It runs off of +5v, using about 5-10mah. There is one configuration jumper to either take power from external 5.5/2.1mm tip-positive power jack, or the TI-99/4A sideport.
I do not have a recommended powersupply.. Generally I use a usb to 5.5mm x 2.1mm barrel converter cable, and whatever the nearest, cheap USB power source I can find.
With this a user can run many of the games on the 2048k cart or any of the 6 multicart games cartridges. Many of the newer cartridge titles also require a 32k expansion and will work with this device.
Bill of Materials
You need the pcboard available from OSHPark, or elsewhere with the gerbers:
schematic pdf - I no longer have the design files for the schematic, and the Copper Connection design tool does not start from schematic. So this PDF is all we have. From an Eagle or Kicad point of view, it is missing the VCC nets.
- pcboard - OSHPark
- Cypress 32k SRAM
- IC SOCKET 20 PIN
- IC SOCKET 14 PIN
- IC SOCKET 16 PIN
- IC SOCKET 28 PIN 0.6”
- 4x 0.1uf ceramic decoupling capacitors
- 2x 1k ohm 1/4 watt resistor
- 10k ohm 1/4 watt resistor
- 680 ohm 1/4 watt resistor
- 3mm RED led
- 2N3904 transistor
- 44 pins of 2.54mm male headers
- 3 pins of 2.54mm male headers - same as above, break off a few.
- header jumper
- 44 single pin sockets
- 44 pin female edge connector ebay seller has various quantities for sale
- DC 2.1x5.5mm power jack
The TI-99/4A speech synthesizer does not pass power on pin #1. However, the 32k memory expansion may be connected to the right of the speech synthesizer and draw power if the power is jumpered across from pin #1 on the left to pin #1 on the right.
Unlike TI sideport devices, this 32k device does not provide an edge connector on the right. Instead the expected expansion mechanism is to use stackable headers for daughter boards, such as are common in the Arduino community. No such expansions exist at this time. The pinout is one for one identical to the sideport of the 4A, except that if using external power, pin #1 passes the external power through.
Omega of Atariage put together an interesting fiction of a possible future which explains this expansion model perfectly. Omega on The Future
The one difference in perspective between myself and Omega’s video is that anyone should feel free to expand on this platform.