BDV11 Bus Terminator/ROM

The BDV11 Bus Terminator/ROM board is a QBUS board that includes:

• bus termination
• bootstrap/diagnostic ROM
• KW11-L Line Time Clock functionality

Physically, it is a quad board, M8012.

Bus termination upgrade

The BDV11 only provides termination for a Q18 QBUS; there is a relatively easy offical DEC ECO (#5) to extend it to Q22, since there are 4 spare resistor networks available in one of the resistor packs. It is:

• Add a wire from BC1 to E1 pin 15
• Add a wire from BD1 to E1 pin 14
• Add a wire from BE1 to E1 pin 13
• Add a wire from BF1 to E1 pin 12

Board layout error

There is a layout error on the BDV11 which can cause damage if a BDV11 is plugged into a system with the optional -12V on pin AB2. The trace which is supposed to connect bus line BIRQ6, on pin AB1, to the pullup network is incorrectly routed to pin AB2. The ECO to repair this (DEC #2 for the BDV11( is again fairly simple:

• Cut the trace (on the solder side) between E1 pin 11 and AB2
• Add a wire (on the component side) between E1 pin 11 and AB1

KW11-L issue

NOTE: Once the KW11-L on a BDV11 has been enabled, RESET/etc do not disable it, unlike every other device in the PDP-11 universe! (This is apparently because they were short a QBUS receiver for the BINIT bus line, and didn't want to add another complete chip to be able to monitor it.) It is, however, disabled by the on-board RESTART switch.

So if you start some operating system which enables the KW11-L (e.g. UNIX), and then try and re-boot it using a front console 'Restart' switch, or by halting the machine and using the 'Go' command to ODT, you'll probably get a clock interrupt in the process of booting, which will trash it.

The only thing that clears it is a manual disable (write 0 to the KW11-L's CSR), using the BDV11's RESTART switch, or power cycling the machine.

Caveat haquur!