[Simh] The Missing PDP-8s

[Mattis Lind]

> The reason there are two DECtape controllers in the current PDP-8
> simulator is that one is block-by-block (TC) and the other is line-by-line
> (TD), where "line" is 3 bits! That means there is a device driver in
> TD-aware PDP-8 software that has to assemble incoming data 3 bits at a time!
>
> The TD8E is dumb but not THAT dumb. It do reassemble 12 bit words for the
processor to deal with.

 http://svn.so-much-stuff.com/svn/trunk/Eagle/projects/DEC/
Mxxx/M868/M868Hsch.pdf

There are three four bit 8271 shift registers that handles it. Both for
reading and writing.
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