11/45 progress

Tony Duell ard at p850ug1.demon.co.uk
Sat Mar 5 18:41:41 CST 2005


> 
> Tony wrote...
> > Odd... That implies your console card is not responding. Maybe it's
> > defective too.
> Kinda what I figured :)

Or alternatively you've got address bus problems too...

> 
> >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
> > the panel.
> Ah ok, good thing I printed off those engineering notes. I'll track down the 
> interrupt enable bit and try that.

My aim (in case you've not guessed) is to try and see if you can write 
even a single bit to a device (or memory) over the Unibus.

> 
> > 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
> > [1] and then try writing to the transmit data registers at 777566 or
> > 777656. See if you can transmit chracters to the terminal.
> I have the appropriate cable from the card to mate & lock, I'll cobble 

That sounds like a current loop cable. Do you have a terminal with a 20mA 
loop input?

If you look at the prints for the M7800, you'll see the transmit output 
of the UART (normally labelled SO -- serial output. I forget the pin 
number, but it's somewhere in the low 20's) goes to the current loop 
driver. It also goes to one section of a 1488 RS232 buffer. 

The RS232 buffer (and the companion 1489 receiver) were not fitted on all 
versions of the DL11. It's worth checking if your card as them, if not, 
they can always be fitted (I think all PCBs have the pads and tracks for 
them), but you may need to fit some extra passives too. If you need to do 
this. I'll dig out my prints and tell you just what to do.

If you do have the RS232 buffer, then you can connect the output of that 
section (which is routed to a pin on the BERG connector) to the RS232 
receive input of a terminal.

> > [1] 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
> > machine...
> Well, as of now, my HP 5315A counter is sitting on top of it :) I'll make 

Right :-)

> the measurements tomorrow. I'm glad you said that, because I noticed the 
> rotary switches for TX & RX speed settings weren't labled (1-10) on the 
> card. This way I can be sure. However, my usual question follows... if I 
> connect to 17 and 40 (separately of course), what is the ground reference 
> location for those measurements? I never seem to know where to hook the 

There is one common ground (0V) rail for the entire machine. It is 
carried over the unibus cables (unlike the power voltages, which are 
separately supplied to each backplane and device). It's also connected to 
the chassis metalwork of the machine

For high-frequency work, you should pick a ground close to the point 
you're measuring since the ground wires do have some impedance. But for 
low frequency tests which this is, you can use any ground in the machine. 
The best one is the ground pin of the chip you're working on, or a chip 
near it on the same board, but I suspect just clipping the ground lead of 
your counter onto the CPU chassis will do.

> other lead :\ In this case, if I can find a pinout for the UART, I'm sure 
> that would be a good spot for ground.

My memory says pin 3, but _please check 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
> > problems.
> Yes, component side of all boards is towards the front, including the two 
> terminators.

OK, good. I hope you don't think I was stating the obvious here, it's 
just that 'silly faults' like that can be a right pain to trace.

-tony




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