7 Aug
2008
7 Aug
'08
2:27 p.m.
From: "Ethan Dicks"
Ever since I got that first PDP-8/L when I was in
high-school, I've
been trying to get a OS/8-capable configuration. I've gotten as
far as an -8/L w/12kW (via a BM08) and PC8L high-speed papertape,
but no posibus mass storage. My negibus -8/i has 64kW of DF32,
but only 4kW of core (another long-term project is to get that up
to 8kW internally).
There are some bus converter projects there too, if those would be
of any help.
On Wed, Aug 06, 2008 at 10:26:08PM -0700, Vincent
Slyngstad wrote:
No particular reason, but the board's pretty crowded trying to get
it all to fit in 8"x11". I'd probably use SIL resistor packs and
shift down the six DIPs below the switches. (I'm not sure there'd
be enough void left to route the thing with 10mil design rules.)
There's some other "fast and loose" stuff in there too -- S240 as
bus drivers, multiple LS loads on the bus (still should be less
than a 74xx load), and (importantly) no provision to continue the
bus, so that it must be placed last. There's also no equivalent
for the G717 terminator card, so it may need to be a fairly short
bus!
Vince
N.B.: The 74LS151's in the write-protect
section need to be real
TTL, and float their inputs high without pull-ups. Of course, if
you don't care about separate write-protect switches for each 32K,
you can just hard wire the inputs to the right values :-).
I don't remember seeing too many designs with floating TTL inputs.
Why no pullups? What's the advantage?