Programmable automation controller (PAC) modules are add-on devices that perform a specific control function in PAC systems. There are many types of PAC modules. Examples include analog I/O modules, digital I/O modules, relay modules, counter modules, serial modules, servo or stepper controller modules, timer modules, and data acquisition modules. Analog I/O modules are used to measure and control industrial automation devices such sensors and actuators. They can also be used to condition high or low voltage signals, thermocouples, resistance temperature detectors (RTD) and strain gauges. Digital I/O PAC modules are used to measure and control industrial automation devices such sensors and actuators. Data acquisition modules digitize and process multiple sensor or signal inputs for monitoring, analyzing and/or controlling systems and processes. A serial PAC module coordinates the flow of data, control signals, and timing information between data terminal equipment (DTE) and data communication equipment (DCE).