ABSTRACT
The hardware of the PIC16F648A-based programmable logic controller (PLC) consists of two parts: the central processor unit (CPU) board and the I/O extension board. The CPU board contains mainly three sections: power, programming, and CPU. The outputs section introduces eight discrete relay outputs for the PIC16F648A-based PLC. Each relay operates with 12 V DC and is driven by an 8-bit serial-to-parallel converter register/driver TPIC6B595 Relays have single-pole double-throw contacts with C (common), NC (normally closed), and NO (normally open) terminals. At the end of each PLC scan cycle, the output data are serially clocked out and finally latched within the TPIC6B595. If there is only one I/O extension board used, then eight clock_out signals are enough to send the eight output signals.
