ard at p850ug1.demon.co.uk
Fri Mar 4 18:35:06 CST 2005
> Ok, found the jumpers for the DL11 in the schematics section on bitsavers. I
> have two M7800's, one is set for 777560 and one is set for 776500.
OK, a farily standard pair of addresses. The former is the console port.
> I'm assuming that when a card is jumpered so (the high bits are constant
> anyways), that it appears exactly at that address no matter how much memory
> is installed in the machine (ie. it doesn't move around based on maxmem).
> Anytime I exam 777560 I get an address error. If I exam 776500, I get a 200,
Odd... That implies your console card is not responding. Maybe it's
> but anytime I store a value and read it back, there's all zero's in the data
You shouldn't be able to read/write all 16 bits -- some of them plain
don't exist in the heardware, some are read-only. But IIRC there's at
least one bit (my memory is weak on this, but I think it's the interrupt
enable bit, maybe bit 6) that you should be able to read and write from
My idea was going to be to hang a terminal off the card (assuming you
have an RS232 lead and can decode the word foramt and baud rate settings
 and then try writing to the transmit data registers at 777566 or
777656. See if you can transmit chracters to the terminal.
 The baurd rate is set by a rotary switch on the card and by the
frequency of the crystal fitted. I found the quickest way to work it out
was to connect a frequncy counter to pin 17 (Rx clock) and 40 (Tx clock)
of the UART chip. Then divide that frequency by 16 to get the baud rate.
But I guess you don't have a frequency counter sitting on top of your
> Methinks the problem wasn't memory, but something amiss in the cpu section.
So do I.
> Bummer as I have no spare cpu cards. But I guess at this point I still don't
I am going to get you to repair that machine properly -- without swapping
boards -- even if I have to get on the next p'lane across the Pond and
show you where to stick your 'scope probe ;-)
> know if it's a unibus problem or a cpu problem.
> Something else I noticed is the terminator cards in front and back as well
> as the cpu backplan to MF11-L had what I would think is a lot of "up down
> wiggle" in them. I'm quite sure they are seated completely, but I can turn
> them up or down more than I would think one should be able to. Is that
You have got them in the right way round, with the resistors towards the
front of the machine, I hope! If not, you will have all sorts of
> Hopefully sage listemembers can offer some advice as to where to go next :)
Ge ta Unibus pinout, grabe the logic probe, and see if the data lines
ever go low on a CPU (frontpanel) write operation.
More information about the cctalk