The PD6124A and 6600A are 4-bit single-chip microcontrollers for infrared remote controllers for TVs, VCRs, stereos, cassette decks, air conditions, etc. These microcontrollers consist of ROM, RAM, a 4-bit parallel-processing ALU, a programmable timer, key input/ output ports, and transmit output ports. Functioning is controlled by a program. A one-time PROM, model PD61P24, to which a program can be written only once is also available. This one-time PROM is ideal for evaluation of programs running in a PD6124A or 6600A, and for small-scale production of such systems.