I/O Relay Modules

An I/O module is a subsystem in an integrated circuit that performs the functionality specific to interfacing a CPU to the rest of the system. It can also refer to configurable switches called I/O relay modules for switching the power to an external load.  It can also refer to a programmable logic controller (PLC) that is used in industrial and manufacturing applications for performing functions like motor control.

I/O modules within a microcontroller or microprocessor are usually memory mapped with registers that store direction, level, type and event information. They may allow interrupts to be mapped to events on configured I/O ports. I/O ports may have multiple function options that can also be configured. PWM and timer capture functions are commonly available, and some I/O banks can support analog signal generation and detection (DAC, ADC). Some I/O modules may support special purpose interfaces (for example, SPI, RS232 serial ports).

I/O relay modules enable a microprocessing system to switch much higher power loads than the I/O pins of the microcontroller can handle while at the same time providing electrical isolation between the same. Isolation is usually by optical photo-diode connection across a barrier or gap. The microcontroller will turn the photodiode on and a transistor base that switches the load will detect the presence of light on the load side. They may incorporate other protection functionality like built-in clamping diodes.

PLCs are rugged modules that usually interface to a microcontroller system via a serial interface like RS485 and will have internal ladder programs that can be configured and combined to enable sensors (for example mechanical encoders) to be read and motors or other devices to be controlled. They may output levels, pulse streams or modulated waveforms (PWM) to control motor speed, positional setting or other characteristics like an ovens temperature.