DLV11 asynchronous serial line interface
It provided both EIA RS-232, and active or passive 20 mA connectivity, at speeds of 110 to 9600 baud; it had vestigial modem control. Line connection was via 40-pin Berg connector headers on the top edge of the card, using the standard DEC asynchronous serial line pinout.
Like the ancestral KL11, the DLV11 has 2 device registers for the receive side (one Control and Status Register - CSR - and one data buffer register), and similarly, two for the transmit side. Each line has two interrupt vectors - again, one receive, and one transmit.
For the PDP-11 main console (which is always a KL11/DL11 compatible device), the standard is that 0777560 is the base address (so the receiver registers are 0777560-2, and the transmitter are 0777564-6), and 060 is the base vector. It can be set to halt the CPU when a 'break' is seen.
The first line after the console is always assigned the address 0776500, and vector 0300. Additional lines are assigned addresses and vectors immediately following, for DL11's #1-#16 (i.e. 0776500-676 and 0300-0476).