User microprogrammability in the HP-21MX minicomputer
W. Gordon Matheson · 1974
The design of a versatile and economical microprogrammable minicomputer is discussed, as embodied in the new HP-21MX computer family. These machines emulate the 2100 line efficiently, yet have a powerful microcode which allows ease of user-microprogramming. 3K words of Control Store addressing space are available for adding special HP firmware options and/or user-generated machine instructions. Some topics to be discussed are: Basic processor organization; Minimization of user concern over processor timing conflict; Interaction with special features such as interrupts, memory protection, and direct memory accesses by the I/O system; Translation of machine instructions into Control Store routine addresses; Organization and execution of microinstructions; Tools available to the user for microprogram development and implementation into ROM or Writeable Control Store.