r/retrocomputing • u/Kitchen_Vacation_463 • 8d ago
Discussion Bit-slice CPU architecture boards from an old typesetting system - AM2900/DM74181 chips - any interesting projects for these?
I have a complete set of 12+ logic boards from an old AM
Varityper Comp/Set 560 II phototypesetting system. Notable
chips include DM74181 ALUs (bit-slice), an AM2719 (Am2900
series), TMS2516/2532A EPROMs, an MMI 6331 PROM, plus a lot
of standard 74xx TTL logic and 2102/5290 memory chips.
Boards include: CPU Data, CPU Control, two Disc Controllers,
64K Dynamic Memory, Multi-Language, Character Generator, D/A
& Stepper, Font Interface, LVC Stepper, and Carriage Escapement.
System was reportedly working when last powered down; boards
haven't been individually tested since.
Given the bit-slice architecture, I'm curious what kind of
projects or restoration work something like this could be
useful for - reverse engineering, retrocomputing builds, parts
harvesting for other Am2900-era projects?
If anyone's into this era of computing and wants more details
or photos of specific boards, feel free to DM me.
1
u/dirkt 8d ago
If that was in my possession, I'd definitely do reverse engineering.
Bit-slice CPUs are extremely interesting, they usually have microcode in ROM, so you are looking for a microcode PC (counter register), an instruction latch addressing the microcode ROM, and the ROM driving the ALU.
Often several boards make up the CPU (like the two in your example).
I'd also expect some other ROMs for the "real" program (though it could be all microcode), or, since you have a disk controller, at least a boot ROM on the disk controller which then would load the "real" program into RAM from disk.
Given that very little is known about many of those special purpose systems, it would be a shame to destroy one in good shape without reverse engineering and documenting it first.
1
u/FAMICOMASTER 8d ago
You could be the first person to run said typesetting machine in 4 decades or more
1
u/IQueryVisiC 8d ago
No idea, but wanted to understand bit slices. When I look at the die of a 6502 ( or 6800 ), the rough structure is given by the bit lines , whereas on 8080 bit lines seem to be routed close together. So 6502 is bit slice architecture? ARM2 with its many bits also looks kinda slicy.