[sdiy] next mistery IC from the junk box - Siemens PSB 2120 (AKA Muscle Man)

[Theo]

On first examination of the junk box with NOS parts I got yesterday
the approx 500 Siemens PSB2120 IC where sorted in the "probably junk"
category.
But some retailers still stock and sell these for around $14.
Makes me curious what they are.

Most in-depth info I could find about the PSB 2120 was this:
http://micro.magnet.fsu.edu/creatures/pages/siemensmuscleman.html

Siemens kindly took the data sheets offline, also no further clues up to
now.
Hints are appreciated :)
I probably put the 2120s on evilbay for $0 but would like to know what they
are first.

Thanks for listening,
Theo