DLV11-J asynchronous serial line interface
It provided both EIA RS-232 or RS-422 connectivity at speeds of 150 to 38.4K baud; receive and transmit speeds are the same on each line, but each line could be set independently. It did not have any modem control.
Like the ancestral KL11, for each line the DL11-J 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.
Normally both the registers and interrupt vectors are in contiguous blocks for the 4 lines, but there are special provisions for one line to be configured as the PDP-11 main console (which is always a KL11/DL11 compatible device). The standard there 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.
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).