1. A microprogram controller for controlling a sequence of one microinstruction to a next microinstruction, comprising: a microprogram counter; continue accessing means for accessing a microinstruction for a next sequential address in microprogram store; branch accessing means for accessing a microinstruction from an address supplied by a current microinstruction; stack accessing means for accessing a microinstruction from an address supplied by a stack; selection means for executing each of respective accessing means in parallel to provide a selected accessed microinstruction, and wherein each of the selected accessed microinstructions comprises: (a) an instruction field, (b) a microinstruction field, and (c) a branch field; means responsive to a selection signal for selecting which one of said three accessed microinstructions is to be executed next in sequence; and control logic means responsive to: (1) said instruction field of a selected accessed microinstruction, and (2) an external status signal for generating a selection signal which is inputted to the selection means for selecting one of the three instructions, said control logic means comprising: means for causing a push branch and continue (PBCT) instruction to be executed, comprising: (i) means for pushing said branch field of said selected microinstruction on to said stack, (ii) means for selecting a microinstuction accessed by said continue accessing means as a next microinstruction to be executed next in sequence, and (iii) means for incrementing said microprogram counter.