S100 Computers - Macrotech -ADIT Board

A non-intelligent I/O board requires the host CPU to spend an inordinate amount of time processing I/O on a character-by-character basis. In small systems with a minimal number of users, this is not a problem. However as the number of users and peripherals increased, especially in an I/O-intensive situation, the host CPU spends so much time on I/O that response time became unacceptably slow even for the 16 bit CPU of the time. When using non-intelligent I/O, every character to be transferred interrupted the host, requiring the CPU's valuable time to save its current state and then process the character. The energies of the CPU were constantly diverted from application processing to handling this steady stream I/O.

The ADIT solved this I/O bottleneck with a 6-MHz Z80 CPU on board and full DMA capability. It had its own on-board "ADIT Operating System" (AOS) and static memory. These features make it possible for the host CPU to off-load a substantial amount of I/O processing onto the ADIT. The host CPU was not interrupted until the ADIT is finished with any assigned I/O tasks. This allowed time-consuming I/O processing to take place in the background, without bogging down the host CPU.

The board of course was completely IEEE-696 compatible. It was a 6 layer PC board. It used eight 8530 UARTS and these could even be configured in synchronous mode. Sample drivers for MP/M-86 and CP/M 2.2 were provided. The 8K ROM on the board housed the "AOS" operating system to run the board. The was 16K or 32K of static RAM on board also to temporally hold data packets.

There was a good review of this board in the S-100 Journal (Vol 1, #5, 1986) see here.
I do not have a copy of the manual for this very useful board. If you can share one please let me know.

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