due to a couple of bugs in the ISDN Blaster PALs, the expansion port is not ready to take any expansions by default
Michael Böhmer from E3B describes the required hardware patch
up to 5 ISDN Blasters can be installed into one Amiga
supported by NetBSD
bugs
the card configures with a chained config request, so the Amiga thinks the card in the slot behind the Blaster is located on the same PIC - this bug is mostly harmless and correctable
the card stores only the upper three bits of the base address, assuming that it will get a place in the address space between 0xe80000 and 0xef0000 - this bug is not correctable
the address decoding does not differentiate between the ISDN chipset and the expansion socket - this bug is only noticeable when an expansion module is present; it is correctable
channel bundling (joining two 64k ISDN lines together for 128k access) is in development
parallel data and telephone calls
CE96 compliant driver
driver (isdnsurfer.device) emulates a Hayes compatible modem
26 pin expansion port compatible with the one on the Buddha/Catweasel controllers
clock port
allows using expansions initially designed for the A1200 clock port
when installed in Zorro slot, pin 40 of the card's clock port is towards the front side of the computer, pin 19 resp. pin 1 towards the rear side
marked wire of clock port expansions go to pin 19 or pin 40, depending on the manufacturer's definition - e.g. expansions made by Individual Computers are installed with the red stripe on pin 40 (to the left), expansions of E3B mark pin 19 / pin 1 (to the right)