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 ECO to extend it to Q22, since there are 4 spare resistor networks available in one of the resistor packs.
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!
