Keyboard controller

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J Booth

Dec 28, 2021, 1:46:39 PM12/28/21
For posterity, I figured I would post some info uncovered on the UNIX PC keyboard. There is a 6850 ACIA on the motherboard which communicates via serial (1200 baud N81) to the keyboard controller which I believe is a MCS-48 microcontroller. My keyboard has a Signetics CP8038 @ 11 MHz, also labeled "80-552871". I was able to find a similar Cortron keyboard for a Burroughs B25 aka NGEN ( that uses a Toshiba 8049 @ 11 MHz, also labeled "80-552871". This leads me to believe the Signetics CP8038 is also an 8049. The 8049 has 2K of ROM, 128 bytes RAM, and 27 I/O ports. The protocol from the keyboard to the 6850 involves injecting some additional characters such as KBD_BEGIN ('0xDF'), MOUSE_BEGIN ('0xCE'), KBD_ALL_UP ('0x40') after no more keys depressed, or the high bit set in a keycode to indicate it's the last character being sent. The 8049 must be responsible for reading data from the mouse (which uses a 6805 @ 4 MHz) and injecting the mouse data within the protocol. The 8049 also receives commands from the 6850 such as reset ('0x92'), turn on/off CAPS LOCK or NUM LOCK LED. (sidenote: 8038 is also a MCS-48 chip, but it has no ROM, so I doubt this is the proper label on the Signetics chip)

Thanks for Phil and AJ, without them I would have little to no knowledge of this.


J Booth

Dec 28, 2021, 2:02:57 PM12/28/21
>> (sidenote: 8038 is also a MCS-48 chip, but it has no ROM, so I doubt this is the proper label on the Signetics chip)

"(CPXXXX) CUSTOM ROM PATTERN NUMBER Applies to masked ROM versions only.
Number will be assigned by Signetics.
Contact Signetics sales office for ROM pattern submission requirements."

So the 8038 must have just been the number assigned by Signetics to the Cortron UNIX PC keyboard 8049 mask ROM. That's my theory at least!

Forgotten Machines

Dec 28, 2021, 5:46:03 PM12/28/21

Most excellent detective work on this, Jesse! And thanks for posting it all here, to be searchable by future UNIX PC enthusiasts...
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