20 Mar
2014
20 Mar
'14
1:59 a.m.
Steve, Vincent, Don: Thank you all. I just knew that the torch was still
lit .... somewhere :->. Any comments that you'd care to make on the
7439-for-8861 substitution?
(And can *anyone* explain the strange GND/Vcc pin choices on the DEC/DS
8640?)
On Wed, Mar 19, 2014 at 11:30 PM, Don North <ak6dn at mindspring.com> wrote:
I did a comparison of the bus input receiver on the
26S10 vs 8641 a while
back.
Here is the plot: http://ak6dn.dyndns.org/stuff/26S10vs8641.jpg
As you can see, there is about a 0.5V difference in the receiver threshold.
May make a difference in some configurations, probably not in most.
Also the 26S10 is a faster device on the bus transmitter output.
This may cause undesired reflections/ringing under some bus loading
conditions.
Ideally the transition time should be longer than the electrical length of
the bus.
With a 26S10 the maximum unibus length would be much shorter than with a
legacy 8641.
Again, may make a difference in some configurations, probably not in most.
Don
-----Original Message-----
fails
From: Vincent Slyngstad <vrs at msn.com>
Sent: Mar 19, 2014 12:07 PM
To: "General Discussion: On-Topic and Off-Topic Posts" <
cctalk at
classiccmp.org>
Subject: Re: DEC Unibus Interface ICs
From: Paul Birkel: Monday, March 17, 2014 12:13 PM
> Unibus Handbook Figure 1-30 does specify the RC-equivalent input for
this
> IC but I have not as yet tried to cross-walk
it against well-known
> SN74xx-series chips. I imagine that I'm the umpteenth person to
encounter
this
problem, so before I try to rediscover fire I'm hoping that someone
else could share their torch of knowledge :->?
I remain a fan of the AM26S10 for this, though like everything else, it to meet the detailed specifications.
Vince