Issue No.10 - October (1971 vol.20)
P.T. Rux , Bell Telephone Lab.
The term microprogramming is most often used to describe the technique of designing a digital computer control unit to execute a sequence of control words called microinstructions. These microinstructions are usually stored in a separate control memory, and each microinstruction usually specifies the machine control signals for one processor cycle time. Husson uses the term microprogramming in this hardware sense and also in a software sense to describe the act of programming the microinstruction sequences.
P.T. Rux, "B71-3 Microprogramming: Principles and Practices", IEEE Transactions on Computers, vol.20, no. 10, pp. 1221-1222, October 1971, doi:10.1109/T-C.1971.223112