Much swearing - was Re: Do-It-Yourself PDP-11 help!

From: Eric Smith <eric_at_brouhaha.com>
Date: Wed Feb 16 17:27:47 2005

I wrote:
> If it's a small enough system to work reliably without termination
> (e.g., a single backplane), it will be fine even with some signals
> terminated. Technically that will introduce a small timing skew,
> but in the small system it won't be enough to matter.

Pete wrote:
> You're assuming the CPU still provides termination at its end. Without
> that, the lines will be floating.

Good point! Here the fact that DEC specially selected low-leakage
driver, receiver and transceiver chips works against you. The
roughly TTL-compatible inputs will pull up for you, but very weakly,
so if there's no termination at either end of the bus, the system may
be unreliable.

Eric
Received on Wed Feb 16 2005 - 17:27:47 GMT