<Compupro made a Z80 slave card that supported between 64K and 256K or RAM <that had a RS-232 port. If I recall correctly you could only put 8 of thes I don't see it in my old catalogs. the closest one was MPX-1 with an 8085, 16k ram, Transient master and interrupts(8259a). Teltek, Konan, Macrotek and SDS did make them however. <There was another method of placing multiple CPU on your bus. That basical <ment building a Single Board Computer (SBC) that could use the S-100 <Temporary Master Access (TMA) hand shaking. The S-100 supported up to 16 o <these TMA on a bus. The advantages is the TMA's tended to use the bus more <efficiently comparied to slaves boards with requried a bus master present <servicing them. I don't know who use to make SBC that fully IEEE 696 <standard for TMA access but do know that they were out there. Been there done that. Used 4 z80s in a symetrical loosely coupled multiprocessing system. One requirement is local and public pool memory that any DMA (device or transient master) can address. Allison