Anyone have a M8340 (EAE) schematic rev.D? Or M8341 rev.D sch?

Kyle Owen kylevowen at
Thu Mar 5 00:56:47 CST 2015

On Wed, Mar 4, 2015 at 5:23 PM, Stephen Lafferty <steve at> wrote:
> We're trying to get an EAE (extended arithmetic element) board set working
> in a PDP-8/e. It turns out that DEC made changes which render M8340 rev.D
> incompatible with M8341 rev.D. (Both of the boards we have are rev.D,
> sigh.) M8340 rev.D requires at least an M8341 rev.E.
> We would like to modify the boards to be compatible but the only schematic
> of M8340 that we've been able to find is rev.F. So it's difficult to figure
> out what changes are needed.
> If anyone has an M8340 schematic earlier than rev.F or an M8341 rev.D sch,
> that would be a huge help.

One small correction: M8340 Rev. D is compatible with M8341 Rev. C and
earlier, from best I can tell from the DEC ECO Log. I don't think there
were many changes between M8341 Rev. D and E.

An M8341 Rev. C schematic would help to establish the differences between
incompatible board sets. If anyone has a Rev. C (or earlier, even) and is
willing to scan both sides, I can attempt to make a schematic. I'm working
on that right now for the M8340 Rev. D.

Right now, obvious differences between M8340 Rev. D and F are that two ICs
have been dropped (both DEC 380s) and a 74H40 has been exchanged for a
74H11. I'm betting that the logic change there created the
incompatibilities they mention. By the way, I did try running these boards
in my 8/M; multiply seems to work fine, but divide returns the wrong
answer. I didn't do any more testing after that (and instead read the ECO
Log and found out the incompatibility reference).

A big thanks to Steve, Chuck D., and Jack R. for their help in providing
boards and pictures so far!


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