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!

So if you start some operating system which enables the KW11-L (e.g. UNIX), and then try and reboot it, 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), or power cycling the machine.

Caveat haquur!