4 Apr
2002
4 Apr
'02
9:50 a.m.
On Thu, 4 Apr 2002, Tony Duell wrote:
The 74x181. I've used it many times. It's also used in many of the
computers that I love (like the classic PERQs and the PDP11/45).
Hytype IIs also use a 8 bit TTL based microcoded machine (IICRC they use
74LS283 adders, 74LS170 register file chips, along with bipolar PROMS)...
Except that every VT52 I've ever worked on used
semiconductor memory, not core.
Anyway. the fact that there's no microprocessor does not mean that
there's no software. There are plenty of microcoded TTL designs about
(the VT52 is one of them IMHO) which have PROMs containing something that
is reasonably called firmware.
Yeah, there is the old 7400 series arithmetic unit...
But in my experience, most pre-micro computer
equipment used fusible-link ROMs for truth-tables;
a transitional item, the Processor Tech SOL's
keyboard, is a good example of this.
Truely microcoded TTL-based designs are not uncommon. The VT52 is
certainly one. So are some of the DECwriters IIRC (but I would have to
check the prints to be sure). DEC seemed to love microcoded designs,
actually...
It's difficult to know just where to draw the line between true
microcoded designs and state machines with the combinatorial part of the
logic in PROMs. In fact I don't think you can really distinguish between
them.
-tony
Peter Wallace