On Tue, Jan 20, 2004 at 10:03:06AM -0800, Michael Sokolov wrote:
Here's my take on the issue of not being able to
use standard drivers and
receivers for UNIBUS and Q-bus. Aren't both of these buses old enough that DEC
made devices for both of them using only discrete logic, no ASICs?
Yes, but some devices are not so old and _do_ use ASICs. There are some
peripherals that came out at the same time as the 11/20 (~1970) that
they are made up of several square feet of TTL/Linear chips.
If they did make UNIBUS and Q-bus devices w/o ASICs
using only standard
discrete logic, as I'm sure they did, what did they use for drivers and
receivers?
Unibus? 8640, 8641, 340, 8881, DC013 (custom DEC chip)
Qbus? DC003, DC004, DC005, DC006, DC010, 74LS240, 8837, 8838
In other words, with few exceptions, *not* ordinary TTL chips (though ISTR
one of their busses used hand-selected 7438s chosen for low (1uA?) leakage.
There are _some_ bus lines that can be loaded/driven by ordinary parts.
However, unlike an ISA card, DEC cards tended towards custom chips of
their own, or designed-as-such bus drivers/receivers from companies like
National Semiconductor.
These are from memory, so if I've made any mistakes, I'm sure someone will
correct me. :-)
-ethan
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