28 Jun
2001
28 Jun
'01
6:38 p.m.
Ethan Dicks wrote:
If you are trying to design a device without the proper handbook and/or
chip-designer's guide, you are probably going to have lots of hidden
gotchas appear unless you happen to clone the bus interface of an existing
design.
Well, I started out intending to do a pretty exact clone of the
standard DEC bus interface, which is when I discovered that some
of the chips just weren't available any more :-(
For COMBOARDs, we used 8641s and DC013s for the UNIBUS
products, and the
real-deal, expensive DC010, DC004, DC005 chips for the QBus product. I
think I remember seeing third-party boards using 74LS240s for bus buffers,
but I do not know how well they'd work in a loaded box (or any VAX newer
than the uVAX-II).
Yes, I thought that a 74LS240 might be OK as a bus receiver so
this sounds plausible. Of course I could always just use 8641's
for everything but this would probably push the chip count up a
bit and right now it's looking as if space will be quite tight
on the particular prototype board that I'm thinking of using.
Thanks for the help.