In computer architecture and engineering, a sequencer or microsequencer generates the addresses used to step through the microprogram of a control store.
It is used as a part of the control unit of a CPU or as a stand-alone generator for address ranges.
Usually the addresses are generated by some combination of a counter, a field from a microinstruction, and some subset of the instruction register.
Most modern CISC processors use a combination of pipelined logic to process lower complexity opcodes which can be completed in one clock cycle, and microcode to implement ones that take multiple clock cycles to complete.
Recent examples of similar open-sourced microsequencer-based processors are the MicroCore Labs MCL86, MCL51, and MCL65 cores which emulate the Intel 8086/8088, 8051 and MOS 6502 instruction sets entirely in microcode.
The model 40 performs no sequential execution of microinstructions and therefore the microsequencer doesn't really branch in the conventional sense.
This format alters the flow of control to 1 of 16 instruction pairs within the low 32 words of a 64-word block of microstore (because bit 5 is always 0).
When the CD field is 0, 1, or 3, flow of control is directed to an instruction within the current 64-word block.