DC319 DLARTs and T11s (was T-11 ....)

Bob Armstrong bob at jfcl.com
Fri Jan 16 09:25:17 CST 2009


>A while ago, Choctaw Bob ]bob099 at centurytel.net] wrote:
>
> [Schematic of Peter McCollum's hand built T11 SBC]
>	Schematic here  http://www.geocities.com/saipan59/dec/t11.jpg

  I just got around to looking at this (sorry - been busy :-) and while it's
nice and simple, it uses a 6850 UART for the console.  It's easy enough to
interface the 6850 (or any other modern UART for that matter) to the T11
bus, but it's not going to be even remotely PDP-11 compatible.  If you want
to have any hope of ever running any real PDP-11 software, you're going to
need a DL11/KL11 compatible console interface.

  For the T11 that means you also want a DC319AA DLART (a "DL-11 compatible
UART chip") chip, and after looking around those seem to be far more
difficult to come by than the DCT11 CPU chips.  Does anybody have a pile of
DC319 chips handy, or know where they can be found?  Unlike the T11 chips,
which can be harvested from a lot of fairly common and not very valuable DEC
boards (e.g. RQDX3s), I don't know of any good donor for DLARTs.  There are
a couple on my FALCON SBC-11/21 board, but I'm hardly willing to take it
apart for this project :-)

  If you can't find a DC319, then the alternative is to build a DL11
compatible interface using a standard UART like the 6402 and a handful of
discrete logic.  I think the minimum you could get away with would be to
implement the DONE and INTERRUPT ENABLE bits (bits 6 and 7) for both the
receiver and transmitter CSR, and then to implement the standard vectors at
60/64.  Oh, and of course the data registers for the transmitter and
receiver.

  The KL11 also implements a MAINTENANCE bit, a BUSY bit, and a READER
ENABLE bit, but a) we have no reader, b) I doubt (I'm hoping) much software
ever looks at the BUSY bit, and c) probably nothing uses the MAINTENANCE bit
except the diagnostics.

  ISTR that DEC had an "official" standard written down for exactly what was
required of a DL-11 compatible serial interface, but I can't find it
anywhere.

Bob





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