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Panasonic KX-TA1232/KX-TD816/KX-TD1232 Hardware Architecture
This article aims to document some of my findings while researching the inner workings of my D816 PABX. While several versions exist for all those models, the general operational principles are, more or less, the same.
Those units have a lot in common and the schematics I could find seem to confirm they're iterations of the same project, even though TA1232 has important differences, like not supporting digital proprietary phones.
CPU and general architecture
The CPU is a classic 68k chip. My unit, particularly, uses a TMP68301AF-12 CPU. According to the datasheet, it's based in the 68HC000 core, produced by Toshiba. It's a 16-bit processor, with 24 addressing lines and 16-bit wide bus.
While the CPU might be different between versions (newer KX-TD models do operate at 12 MHz, in contraposition to older models at 8 MHz), the pinout seems to be largely the same in all three versions.
| KX-TD1232CE/1232BX etc. | KX-TD816E (UK) | KX-TA1232 |
|---|---|---|
 |  |  |
This PABX is, in fact, a simple, embedded m68k computer. Memory and peripherals are addressed directly, there's no MMU. Also, albeit the system has a 16-bit wide bus, it looks like only the memory chips are using all those lines (see diagram below.) All other devices I saw were using only eight lines of the data bus. Addressing lines seems also to go under-used for most devices, e.g. expansion cards using A1-A5, or even the Caller ID card, using A1 and A5, ignoring all others.
Memory
Those systems seem to be typically equipped with four RAM and two ROM chips. TA1232's Service Manual seems to suggest they might not be always populated. On my TD816BX, they are. Intriguingly enough, they didn't …………
Caller Identification Card
As this investigation progresses, I might transfer this section to it's own article, since it's a bit of a rabbit hole.
The digital PABX's (KX-TD) got the KX-TD193 or TD193X as their standard Caller ID add-on card. This part features pretty standard FSK modems that output serial date for two serial-to-parallel converters, that then feed data to the system bus.
Funnily enough, there's a second card for KX-TD systems called KX-TD193DX, that also does DTMF (hence the extra «D» in the name, I guess), and this card also happens to be nearly identical to the TA-123293 card, which also had DTMF decoding facilities. The only significative difference I could spot was an extra IC, which communicated with TA1232 via four extra pins that KX-TD's don't have.
