4 Mar
2014
4 Mar
'14
3:14 p.m.
On Tue, Mar 4, 2014 at 2:26 PM, Kyle Owen <kylevowen at gmail.com> wrote:
On Tue, Mar 4, 2014 at 3:05 PM, Marc Howard
<cramcram at gmail.com> wrote:
The low speed and use of standard TTL does cover a multitude of sins. The
problem I worry about is when you mix contemporary devices with old school
logic. What looks like harmless ringing in 70's TTL land can look like a
clock pulse to modern CMOS device. But you're right, the PDP8 stuff works
(for the most part) with two layer boards, rather simple bypassing, and not
much impedance control.
Marc
I just don't want to see someone doing a good
deed get burned. Another
suggestion is that as long as he's doing this it should probably be a 4
layer board. Doesn't increase the price that much and does wonders for
signal integrity.
Why would four layers be a concern, though? All of the boards in my PDP-8/E
and /M boards are two-layer, with manually routed traces and no ground
plane.