A Bit-Slice Microprocessor System for Teaching Microprogramming

This paper describes a microprocessor development system, which was designed for demonstrating the use of bit-slice microprocessors, for teaching microprogramming and for simulating other small microprocessors. The system contains two 2901 bit-slice microprocessors together with the necessary control and sequencing logic, a 256 × 56 bit microprogram control memory, a macromemory with associated address and interface registers, and an interface to an MDS-80 microcomputer development system. A monitor program which runs on the MDS-80 controls the execution of the 2901 microprograms. This monitor provides for loading microprograms, examining and changing both the microprogram and macroprogram memory, examining and changing 2901 internal registers, setting breakpoints, and tracing microprogram execution. The monitor also provides an interactive editor for altering microprograms. A cross-assembler for the 2901 microcode was also developed. This cross-assembler accepts inputs in a register-transfer format and generates the 56-bit wide microcode words ready for loading into the 2901 control memory. Student projects which have been completed using the system range in difficulty from a binary multiplier to an emulator for the M6800 microprocessor instruction set. The system is easy to use, is relatively low in cost, and has proven to be a valuable educational tool.