M105 Address Selector
It was used, along with an M782 Interrupt Control, in early PDP-11 device controllers which plugged into an SPC slot. It was also used in a number of early devices which were built out of a custom backplane and a large number of FLIP CHIPs, such as the RK11-C. Some later devices which no longer used a large number of small Flip Chips (such as the TMB11) also used it.
The board contained a number of jumpers which could be use to set the address to be recognized; the jumpers apply to UNIBUS address bits 3-12. The M105 recognizes any address within a eight byte block; if a device needs more than 4 word registers, the M105 cannot accomplish that.