PDP-11/84 SLU problem?

Pete Turnbull pete at dunnington.plus.com
Mon Dec 15 13:40:06 CST 2014

On 15/12/2014 18:47, Noel Chiappa wrote:
>> From: John Rollins it doesn't appear to transmit data from the
>> console port on the back. I have tried ... every conceivable switch
>> setting on the PDP with nothing

> I asssume you've tried setting the baud rate with the switches on the
> CPU card (in case the cable to the back panel is damaged - or, more
> likely, the rotary baud select switch has a bad contact due to
> corrosion over time)?

The normal setting is all 8 switches in the pack at E83 (beside the 
LEDs) off.  Switch 1 is to do with the console SLU (see below).  2, 3 
and 4 set the boot device (all off means boot according to the settings 
in the EEPROM; all on means power up in ODT providing switch 1 is off). 
  Switch 5 is the "force dialog mode" switch - on an 11/83, setting 1 
and 5 on is used to "disable customer access to setup", to prevent the 
most common cause of the not booting correctly problem.  If switch 5 is 
on, the CPU won't go into dialog mode.  6, 7, and 8 set the baud rate, 
providing the rotary switch on the panel is either disconnected or set 
to 7 or set to 15.  For 9600 set 6 and 8 on, 7 off; for 1200 set 7 on, 6 
and 8 off.  All on is 38400; all off is 300.

> If you have the parts, fabricating a substitute serial interface
> cable would also be something to try.

Always a a useful device for QBus machines.  The same cable fits 
KDF11-B, KDJ11-B, DLV11-J, MXV11-A, MXV11-B, etc.

> The next step would normally be to disable the on-board serial
> interface, and provide a substitute console interface, out on the
> bus. _Alas_, as far as I can tell from reading the KDB11-B User's
> Guide (EK-KDJ1B-UG-001), there is no way to disable the on-board
> serial interface.

Actually, setting switch 1 (in the pack at E83, beside the LEDs) on 
should disable the console, but I know that at least on early boards it 
doesn't (wasn't implemented) and I can't remember if that's a hardware 
issue or a ROM function.


Pete Turnbull

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