Yeah, but look at it this way: their being inverted can be a memory jogger - 'Oh, the DL11, that effed-up interface where the jumper sense is inverted between address and vector!' Then you only have to look up one of the two.. :-) "Terminal" != "console". (Or, rather, the latter is a unitary subset of the former.) The 'system console' is, by definition, on all PDP-11's, a DL11-type serial interface at 777560. However, it may have many 'terminals'! :-) Sort of (unless you mean 'instead of 777560/60, you meant 60/64, right?'). 777560 is the base address, 60 is the base vector. The receiver registers are 777560-2, and the transmitter are 777564-6, but on the DL11, one can only set the base of the entire group of 4 registers, one can't move the transmit and receive around independently. Similarly for the vector, one can only set the base; the receive (B) and transmit (B+4) are paired in the hardware. Hence, "777560/60". Noel