Purchase a CX85 Numeric Keyboard Board for the 1090 XL Expansion System Replica (10-15 mins)

Task: Purchase a CX85 Numeric Keyboard Board for the 1090 XL Expansion System Replica

Needed: Web browser, Atari XL or XE, CX85 numeric keyboard

Time: 10-15 minutes


I recently posted about the newly developed 1090 XL Expansion System replica for connecting devices to an Atari XL or XE computer through the Peripheral Bus Interface or PBI located on the back of the computer. I also recently posted about displaying text in 80 columns using a special board for this device that outputs video in HDMI. The next board for this device I tried is the CX85 numeric keyboard board that allows this standalone keyboard to be used without occupying the joystick port and without the need to manually load the driver from disk. As noted in this article from Compute! Magazine in 1983, the CX85 was designed for use with the Atari Bookkeeper software for accounting.

The Atari CX85 Numeric Keyboard
The Atari CX85 Numeric Keyboard


First, purchase the 1090 expansion board from Tindie for $85. Thanks Brian Reifsnyder and Ken Ames for making this possible.

Second, purchase the CX85 expansion card for $75 each. This is an option on the main board page. The card is pictured below plugged into the main board.

Third, installing the main board unit (pictured to right below) is easy. You will need a 9V power adapter (e.g. like the one used for the Atari 800 and 1050) that plugs into the back of the main board next to the power switch. The unit comes with a ribbon cable that plugs into the PBI slot on the back of the 800XL e.g. Pop off the protective cover first.

CX85 expansion board
CX85 expansion board

Fourth, plug in the CX85 board in an open slot with the joystick port facing back toward the power switch.

Fifth, optionally, you can also plug in the 80-column board for HDMI text out to an LED. You can see this board behind the CX85 board above.

Sixth, power the 1090 board on and then boot your Atari. If all works you should be able to type numeric text from the CX85 keyboard as shown below.

Text typed in BASIC XE using the CX85 keyboard
Text typed in BASIC XE using the CX85 keyboard


I am not sure why anyone would want to use a CX85 these days. However, this was really fun and allowed me to dust off my CX85 keyboard and give it a spin. This is the first time I have used this since the 1980s.

You will of course need a CX85 keyboard for this project. I was lucky enough to still have mine. I checked on eBay and was surprised to only find one for sale with another included in an Atari 800 lot. Good luck finding one!

Note that the driver for the CX85 is included on the board and does not need to be loaded from disk.

Here is the user manual for the CX85. Here is the field service manual.

The CX85 keys could be reprogrammed with some POKEs or by changing the drive code. The ROM on this board does not support that function.

The driver and the CX85 master disk ATRs can be found here.