1.2 AN EXAMPLE OF A COMPUTER IN MANUFACTURING

• PLC’s are an example of a microcomputer used for industrial control

• The basic components in a PLC are,

- CPU

- RAM to store working variables, statuses, etc.

- ROM to store the operating system, and programs for interpreting ladder logic, programming, etc.

- A/D, D/A - To input and output analog signals from the PLC, these I/O devices are used

- PIA (Parallel Interface Adapter) - used to drive parallel data lines for digital I/O. These lines are used for detecting switch closures, driving relays for outputs, turning indicator lights on and off, etc.

- ACIA (Asynchronous Communications Interface Adaptor) - used to drive RS-232 ports (or other serial ports) for interface.