Category Archives: AVM T1

Hacking the AVM T1


It was inevitable… the biggest system AVM built was the “T1”, a 30 channel ISDN controller in a sleek 1U 19 inch case of which nothing more than the above marketing picture seems to exist.
One fine day I had to had one – and today is the day!

I was able to find a AVM T1 on ePay which was not very well advertised so I had no “professional competition”. Even I didn’t spent a fortune it was a bit of gambling because I didn’t knew what to expect.
Besides AVMs own T1 PDF manual there’s next to nothing available in the Web – So this section is yet another WWW-exclusive brought to you by 😉 (Ok since 2009 others discovered this page and also this cheap entry into the wonderful world of multi Transputing)
Still, the docs said “a Transputer network with 9MB RAM” so I couldn’t go completely wrong. That said, I was expecting SMD T400s at AVMs usual sluggish speed…

First look

When the box arrived first thing was getting out good ol’ screwdriver and open the case…


…and I was very surprised:

  1. A socketed T425 – so that’s another easy upgrade then.
  2. An external power supply (48V)! That’s strange but also neat – no noise and next to no heat in the case itself
  3. Also, the board is very small…  lot’s of room left in the case.

That’s done by intention as you could buy the T1-B, where “B” stands for the “Booster Board”, yet another board with 4 more Transputers and another 8MB of RAM giving a total of 7 Transputers and 17 Megs of memory. Quite a setup for just an ISDN controller.

Sniffing around

Ok, this beast has to do something better than handling 30 boring B-Channels… Mandelbrot for example 😉 So let’s see how this thing is/was supposed to speak to the outside world.

The manual is talking about an ISA or PCI controller-card which will be connected to a 9-pin Sub-D connector. Having a closer look to the mainboard where that connector is seated I discovered some other old friends: AM26C31 and AM26C32.
Aaaaalrighty, RS422 time… that’s the same way my Tower of Power is transmitting its data. So I can use my TTL-to-RS422-converter I’ve built for the Gerlach card.

Out goes the multimeter and after a while I figured out the the traces on the board. For a better understanding, here’s the “map”:


Marked by the red arrows are the three Transputers:  T1, a T425-25, is the “application processor” while T2 and T3 are more simple T400-20 handling the ISDN subsystem.

The yellow arrows mark the four links of the T425 – which is probably the reason why AVM used a 425 vs. their usual T400: this time they really needed 4 links.
Link0 is connected to the 9-pin sub-D connector (via the RS-422 transmitters/receiver) for interfacing to the PC.
Link1 and Link2 are directly connected to the T400s.
Link3 goes to the connector on the lower edge of the board. I bet this is where the “booster board” would be connected… not a hard bet, I admit.

The pinout for the 9-pin sub-D connector (female) is:

 1 Link0-IN -
 2 N/C
 3 Reset-IN +
 4 N/C
 5 Link0-OUT +
 6 Link0-IN +
 7 Reset-IN -
 8 GND
 9 Link0-OUT -

As Link0-IN and Reset-IN are routed through two separate 26c32 I assume there might be more differential signals available. If time allows I’ll dig deeper on this matter.

Do something Gromit!

Well then… a cable was built in a couple of minutes – some cursing and swearing about the differential polarity and then the exciting moment came: Let’s see if it’s really so easy again!

It is! And here’s the ispy output for the T1 (connected to the “Gerlach card”):

Using 150 ispy 3.23 | mtest 3.22
# Part rate Link# [  Link0  Link1  Link2  Link3 ] RAM,cycle
0 T800d-25 288k 0 [   HOST    …    …    1:0 ] 4K,1 1024K,3;
1 T425c-20 1.6M 0 [    0:3    2:0    3:0    … ] 4K,1 4092K,3.
2 T400c-20 1.7M 0 [    1:1    …    …    … ] 2K,1 1022K,3.
3 T400c-20 1.8M 0 [    1:2    …    …    … ] 2K,1 4094K,3.

Some remarks about this:

  • 9 MB is true. The “application processor” (T1) got 4MB while the two T400s got 1 (T2) and 4 MB (T3, obviously connected to the SIEMENS Munich32 Über-ISDN controller).
  • While the built-in T425 is spec’ed for 25Mhz it’s just running at 20MHz… what a waste of bang… and what an opportunity for improvement :->
  • The linkspeed is at maximum… which one would expect with directly connected links. But with AVM you’ll never know 😉
  • The RAM-speed is pretty good (compared to what they did to the B1) – even they just used 70ns RAM.

Next up: Having fun with Mandelbrot! Having just T4xx Transputers it can only use the integer algorithms (i.e. no floating point) but who cares for a quick start?!

It’s working and showed another nice gadget: LEDs! Each Transputer has a tiny SMD-LED connected to it’s Link-Out.
So having the T1 underneath the table I have quite a nice light-show while the three are working their a** off 😉

Here’s a video of Transputer-driven-Blinkenlights:

If you happen to have no access to a RS422 converter: Never say die!
Like said above, there’s still Link3 available – normally meant for the booster-board – and it’s pure TTL. All you need is a somewhat non-standard plug to this connector. Be creative but don’t forget that unbuffered link connections only allow a distance of a couple of inches/centimeters!

The pin-out (so far) is, counting from left to right:

 1 - 5V VCC
 2 - T1 Link3 OUT
 3 - T1 Link3 IN
 4 - RESET
 5 - T3 Link1 OUT
 6 - T3 Link1 IN
 7 - GND

[UPDATE 11/14/10] Again, with some ePay-Luck I got another T1… and it again was some kind of lottery… and I had luck! This time it’s a T1-B!! This means, the “booster board” is installed. So opening the case, it looks like this. On the right the normal T1-board, to the left, “da mighty booster board” 😉 I’ll call it “BB” from here…T1-Booster-Full

As expected, it’s connected via Link-3 of the T1 Board. On the lower edge of the picture you can spot the power-supply “module”. It’s longer than in the T1 configuration and provides 3.3V/GND to the BB, i.e. the BB is 3.3v only!!

Here’s the BB alone:


All in all the BB is more modern than the T1-board. Very suspicious are the JTAG connector on the lower left having its lines connected to a EEPROM (AT28V256, right edge of the BB board, above the row of RAMs). Further up, left to the CPU nearby is a pad with the lable “Boot from ROM/Link”. I wonder what the default is and what’s inside that EEPROM – will investigate later.

Most importantly the BB board features 4 ST20450 processors, which aren’t INMOS products anymore. They were designed by ST after they bought INMOS. For short, the ST20450 is a T425 on steroids. More on-chip RAM (16K), higher clocking (40MHz) and some more instructions.
Each ST20450 has its own 2MB of RAM and a GAL handling the memory etc.. Here’s a close-up of a single ST20450 “module”:


Mind the careful markings/labels on the board. The CPUs are numbered (“Processor 3”) and there are pads for Links etc.

Finally, I currently have no tools to check/use ST20450 processors. ispy finds the Transputers on the T1 board but freaks-out when it pings the ST20s.

Here’s another new addition: A picture of the official T1-PCI interface. It contains a PCI-controller (the big IC) and a XILINX FPGA… probably containing a synthesized C011.



Jonathan Schilling also playsplayed around with a AVM T1 including the original ISA controller card… and he‘s making made very good progress! Check out his page over here (German)!
[2015, Jonathan quit ‘the scene’ and handed over all his equipment]


  • Change the T425
  • Make the 30 front-panel LEDs blink
  • Figure out for what the female 15pin sub-d connector is good for (not mentioned in the manual)

Here’s how to access the LEDs at the front – thanks to Michael Brüstles research:

typedef unsigned long int u32;

 *  wr                               0-01    __ EN __ __-__ __ __ SY
 *  wr                               0-10    08 07 06 05-04 03 02 01
 *  wr                               0-11    16 15 14 13-12 11 10 09
 *  wr                               1-00    24 23 22 21-20 19 18 17
 *  wr                               1-01    SC ST 30 29-28 27 26 25
 *  rd                               0-01    readable ... content unknown

int main( void ) {

    u32 *p = (u32*)0x80700000UL;

    p[ 1 ] = 0x40;  /* enable all leds 0x40 & Sync 0x01 */
    p[ 2 ] = 0x05;  /* Led01-Led08 */
    p[ 3 ] = 0x00;  /* Led09-Led16 */
    p[ 4 ] = 0x3F;  /* Led17-Led24 */
    p[ 5 ] = 0x92;  /* Led25-Led30, System, S-channel */

    return 0;