RTC-SIR is a multifunction expansion board offering a combination of four independent I/O subsystems: bidirectional TTL parallel I/O, RS-232 serial I/O, infrared transmit and receive, and 16-bit programmable timers. The parallel I/O consists of 24 bits of TTL from an 8255 PPI. The RS-232 serial I/O consists of an independent UART and timebase which provide all standard data rates from 50 to 38,400 bps. The onboard infrared transceiver consists of a 40-kHz modulated or digital on/off infrared transmitter and 40-kHz fixed-frequency receiver. Finally, for precision timing, the RTC-SIR is fitted with the 8254 programmable timer, giving it three independent 16-bit binary or BCD counter/timers.