MITS 2SIO serial chip?

From: ajp166 <>
Date: Sun Dec 16 14:37:57 2001

-----Original Message-----
From: Ben Franchuk <>
>> Sure its trivial to do now but we were talking 1981 when PALS were
>> expensive.

Yes, they were compared to random logic, but if board space was costly
they were cheaper.

>I never heard about pal's until about 1990. In some ways the peripheral

PALS are 1970s technology, really old to some of us.

>chips are in a really sorry shape. You have vintage slow I/O (2 MHZ?)
>or PC motherboard chip sets. Nothing in between. On my FPGA I can run
>with a 250 ns memory cycle, but need to stretch it to 625 ns for I/O.

Actually thats not true. BY 1981 you have peripherals in the 125ns read
write timing range. Then again Z80 at that time was just hinting at 6mhz
so z80 peripherals were of an according spped for that cpu. However,
parts were faster and often far cheaper.

Personally if I wanted the SIO functionality for a NON-z80 system I'd
never use the zilog part. Reason it was not cheap,nor was it easy to
use for non-z80 systems. They were designed for the Z80, period.
Unfortunatly they were slow. If you wanted faster the 83xx or 85xx
parts from Zilog were a far better choice but Zbus was scary to most
people and they weren't cheap. The other part of this is NEC and
Intel did the MPSC (NEC D7201, INtel 8274) which was functionally
identical to the SIO and was "tuned" for 8080/8085/8088/8086 style
busses and faster as well. It was a more generic part than the SIO.
Also around that time Signetics and friends were doing the 2681 part
that was cheap and available in various flavors. Peripherals back then
were quite varied.

Received on Sun Dec 16 2001 - 14:37:57 GMT

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