Interruptible microprogram sequencing unit and microprogrammed apparatus utilizing same

A microprogrammed apparatus comprising a plurality of data paths for manipulating data, a control memory connected to said data paths for sequentially providing a plurality of addressable microinstructions contained in said memory to said data paths for controlling said data paths, and a microprogram sequencing unit connected to said control memory for providing a sequence of microinstruction addresses to said control memory, said microinstruction sequencing unit including an address output for providing addressing microinstruction addresses to said control memory, an address bus connected to said address output such that a plurality of microinstruction addresses applied to said address bus are sequentially provided to said address output, means connected to said address bus for applying said plurality of microinstruction addresses to said address bus, an interrupt return register operably connected to said address bus for receiving a microinstruction address from said address bus and storing said received microinstruction address, and means connected to said address bus for interrupting said sequence of microinstruction addresses and effecting storage of a microinstruction address on said address bus in said interrupt return register.