Subject: DC319 DLARTs and T11s (was T-11 ....) From: "Bob Armstrong" <bob at jfcl.com> Date: Fri, 16 Jan 2009 07:25:17 -0800 To: <cctalk at classiccmp.org> 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