TD816/TD1232 are equipped with one/two serial port(s). This primarily serves the SMDR facility, which records outside calls (and, probably, whatever calls you want to record, the manual is extensive and I don't know for sure.) However, the RS232C port can also be used for remote programming.

Connecting the KSU to the computer is dead easy. The installation manual has instructions and even the pinouts to make it work. It's a bog standard RS-232 null cable, male DB-25 to female DB-9. Once connected, you can use PuTTY, HyperTerminal or the likes to get it connected. By default, the settings are: 9600bps, 8 bits, 1 stop bit and «mark» parity. You may want to activate RTS/CTS as well. Do that, and you get a text string that's probably something like this:

ATQ0E0V1S0=1X0&D0

This has a function, but let's leave at it, for now. If you see it, you're successfully connected and will probably get SMDR records on your terminal.

Now that's where the walk in the park ends. There's absolutely no documentation available for this unit on what comes to remote programming. You'll see mentions to the «System Programming and Diagnosis with Personal Computer» on the Features Guide, but not elsewhere is this document to be found. And nearly every forum post you'll stumble across will be like «wHaT ArE yOu TRyInG to DO? JuST uSE thE ProPRiETaRy teLePhoNe To PRoGrAm» or «do you need the XPTOXKCDWHTVR-4 version? sent you via PM.» I can't begin to surmise why is the telephony/PBX world so walled. Not even HVAC world is so protective of itself.

So, you see, I'm writing this out of sheer frustration. But it gets worse. I was able to track down some of the programming software (cf. here, in the «Software» session) originally used by sales representatives. So, here it is:

It works? Ehhhhhhh… Kind of.

It will connect to the system, but then will throw you some curveballs, as exemplified in this sequence, in which trying to get to the first group of configurations for the extensions will show a blinking message about «Saving system data» (despite nothing having been altered) and finally throw a «Parameter Error»:

Albeit I certainly didn't test it nearly quite enough to assert how widespread the problem is, it's clear by now that this software isn't exactly a match to my TD816BX's P401A ROM. And the first version was what worked better. Versions 2, 3 and 4 would throw «Database mismatch» errors left and right. This makes sense, this ROM seems to be quite old (dating back to 1996) and, to make matters worse, this software is probably tailor made for the British version (TD816E/TD1232E.)

Nevertheless, some sections do work and I suspect you can easily do some basic changes, like time and date. And this was sufficient pretext to throw me into a whole new rabbit hole: to understand how the software communicates with the PBX and maybe learn something in the process.