Andy:
Note that many many ISDN modems, terminal adapters, call control units (CCU's), line monitors, and conferencing units have used the Motorola MC68302 processor to run the protocol stack. I am of the opinion however, if you used a high speed 1X clocked processor such as a Cygnal part at 50 MHz and had about 64K of FLASH you should be able to run the Link Technology stack on it. We ran it on a 15.36 MHz MC86332 processor supporting three simultaneous phone lines (three D channels) and it took only a small percentage of the software bandwidth. After all D channel data only flows at 16K bits per second. I think a Cygnal would work fine if the TDM was externally interfaced in a HDLC controller. Another nice choice would be a Triscend with the programmable logic made into a TDM interface and HDLC controller.

The thing I would avoid trying to do on the microcontroller is a software implementation of HDLC but even a table driven design of that uses more FLASH than processor bandwidth.

Clearly the best thing is to talk directly to the ISDN protocol stack providers. Then can tell you right away what kind of processor capacity is needed for their stack implemenation. Note we had used LinkTechnology because of the personal level of service we got from a small company as opposed to the larger companies. Sometimes a larger company IP provider that does many product categories can be slow on the support turnaround time. Link was always right there to help us even though they were 1000 miles away.

Michael Karas