Abstract: A microprogram load unit comprising a readable and writable microprogram memory within a central processor unit for storing microprogram, a relatively low speed, readable and writable, nonvolatile memory unit, and a readable and writable memory with battery backup. It is determined whether data of the readable and writable memory with backup has been lost or not when power is turned on. If data loss is not present, microprogram is read out of the readable and writable memory with backup and written into the microprogram memory. If data loss is present, microprogram is read out of the nonvolatile memory unit and is written into the microprogram memory.

Abstract: A microprogram load unit comprising a readable and writable microprogram memory within a central processor unit for storing microprogram, a relatively low speed, readable and writable, nonvolatile memory unit, and a readable and writable memory with battery backup. It is determined whether data of the readable and writable memory with backup has been lost or not when power is turned on. If data loss is not present, microprogram is read out of the readable and writable memory with backup and written into the microprogram memory. If data loss is present, microprogram is read out of the nonvolatile memory unit and is written into the microprogram memory.

Abstract: A programmable controller for controlling a plant on the basis of a stored program includes a processing unit for reading out an instruction from a program memory to process the instruction. In the processing unit, it is determined whether the instruction read out from the memory is an instruction taking a register-modified addressing mode or an instruction taking a direct addressing mode. When the read-out instruction is an instruction taking the direct addressing mode, a plant is directly addressed by the address part of the instruction. Then, an arithmetic operation is performed using the state information which is read out from the plant thus addressed, or plant control information is sent from the processing unit to the plant thus addressed.