Copyright © 2002 Delmar Thomson Learning Chapter 10 PLC Processors
Copyright © 2002 Delmar Thomson Learning Objectives Describe the function of the processor. Describe processor operating modes. Explain the function of the watchdog timer.
Copyright © 2002 Delmar Thomson Learning The PLC Processor The processor is a digital computer that reads inputs, solves the ladder logic, and updates the output field devices. Processors are available with differing capabilities within a specific PLC family. Processors have different operating modes.
Copyright © 2002 Delmar Thomson Learning Processor Operating Cycle Processor is designed to perform specific duties in a specific sequence. This operating cycle is called the processors scan or sweep. In run mode, the operating sequence is continuous. Operating cycle consists of numerous steps.
Copyright © 2002 Delmar Thomson Learning Input Scan During the input scan, the processor scans each input module for the on or off states of each input point. Input status information is stored in the input status file.
Copyright © 2002 Delmar Thomson Learning Program Scan Processor scans ladder program starting at rung zero at the left power rail, working left to right, evaluating one instruction at a time until the output instruction is reached. The output instruction will be either true or false.
Copyright © 2002 Delmar Thomson Learning Program Scan (cont’d.) A logical 1 or 0 will be placed in the output status table address referenced by the particular output instruction. With rung completed, processor goes on to the next rung, sequentially until the last rung of the program has been executed.
Copyright © 2002 Delmar Thomson Learning Output Scan The output scan is where the processor writes the on or off status, one word at a time, to the associated output module. Output module updates each field device’s status.
Copyright © 2002 Delmar Thomson Learning Service Communications After all output modules have been updated, the processor services communications. Updates handheld or personal computer monitor screens. Sends communications to other devices on the network.
Copyright © 2002 Delmar Thomson Learning Reset Watch-Dog Timer Last part of scan is to reset the watch- dog timer. Watch-dog timer ensures current scan is complete. When watch-dog timer is reset, the scan starts over.
Copyright © 2002 Delmar Thomson Learning Serial Communications Simplest method to communicate between a PLC processor and a computer is serial communications. Connect proper serial cable between computer’s COM port and processor’s RS-232 communications port. Not all processors have RS-232 communications port.
Copyright © 2002 Delmar Thomson Learning Selecting Proper RS-232 Interface Cable Most serial communication problems between computer and PLC are due to incorrect cable. Two types of serial cables: Straight through cable Null-modem cable
Copyright © 2002 Delmar Thomson Learning Straight Through Cabling between Computer and Peripheral Equipment
Copyright © 2002 Delmar Thomson Learning Straight Through Serial Cable Straight through serial cable all wires go through the cable without crossing. Wires are identified as pin numbers. Pin 2 goes straight through to pin 2. Pin 3 goes straight through to pin 3. Used when intermediate communication device between two computers.
Copyright © 2002 Delmar Thomson Learning Directly Connecting Computers with a Straight Through Cable Both computers sending information out on pin 2. Computers expecting information on pin 3. Communication will not be successful.
Copyright © 2002 Delmar Thomson Learning Connecting Two Computers with a Straight Through Cable
Copyright © 2002 Delmar Thomson Learning Null-Modem Cable Wired so Pin 2 Crosses to Pin 3 Pin 2 physically crosses to pin 3 in cable. Information sent from computer crosses from pin 2 to pin 3 so it can be received by other computer device. Communication is successful.
Copyright © 2002 Delmar Thomson Learning Null-Modem Cable Crosses Pin 2 to Pin 3
Copyright © 2002 Delmar Thomson Learning PLC Processors Have Multiple Operating Modes Processor has two modes of operation: Program mode Some variation of run mode
Copyright © 2002 Delmar Thomson Learning Program Mode In program mode, the processor is accepting new instructions, either as a new program, or as changes (edits) to an existing program.
Copyright © 2002 Delmar Thomson Learning Run Mode When the creating or editing of a program is complete, the processor is put into run mode to run or execute the program. In run mode, the processor executes the operating cycle called the scan or sweep.
Copyright © 2002 Delmar Thomson Learning Remote Run Mode Some processors have key switches on processor module to change operating modes. Changing operating mode to run or program using key switch is called local mode. Changing operating mode from a personal or industrial computer through a communications cable is remote mode.
Copyright © 2002 Delmar Thomson Learning Remote Program Mode If processor put into program mode from a remote programming device, this is called remote program mode. The remote computer device can perform any programming operations remotely. When completed, processor can be returned to remote run mode to execute PLC program.
Copyright © 2002 Delmar Thomson Learning Test Mode Test mode is used to test a program during installation, maintenance, or troubleshooting. Test mode reads inputs and solves ladder program, but does not allow field devices to be energized.
Copyright © 2002 Delmar Thomson Learning Processor Communications The physical connection between a processor and the outside world is called a communication port.
Copyright © 2002 Delmar Thomson Learning SLC 500 Processor Communication Capabilities MicroLogix 1000 DH-485 and Ethernet 5/01 processor DH-485 5/02 processor DH-485
Copyright © 2002 Delmar Thomson Learning SLC 500 Processor Communication Capabilities (cont’d.) 5/03 Processor Serial and DH-485 5/04 Processor Serial and DH Plus 5/05 Processor Serial and Ethernet
Copyright © 2002 Delmar Thomson Learning SLC 5/03 and 5/04 Communication Ports Image courtesy of Allen-Bradley, a Rockwell Automation business
Copyright © 2002 Delmar Thomson Learning Processor Capabilities A processor’s capabilities are determined by Memory size Instruction set I/O supported Communication ports
Copyright © 2002 Delmar Thomson Learning SLC 5/01 Processor Specifications Image courtesy of Allen-Bradley, a Rockwell Automation business
Copyright © 2002 Delmar Thomson Learning SLC 5/02 Processor Specifications Image courtesy of Allen-Bradley, a Rockwell Automation business
Copyright © 2002 Delmar Thomson Learning SLC 5/02 Processor Image courtesy of Allen-Bradley, a Rockwell Automation business
Copyright © 2002 Delmar Thomson Learning SLC 5/03 Processor Image courtesy of Allen-Bradley, a Rockwell Automation business
Copyright © 2002 Delmar Thomson Learning SLC 5/04 Specifications Image courtesy of Allen-Bradley, a Rockwell Automation business
Copyright © 2002 Delmar Thomson Learning SLC 5/04 Processor Image courtesy of Allen-Bradley, a Rockwell Automation business
Copyright © 2002 Delmar Thomson Learning SLC 5/05 Processor Specifications Image courtesy of Allen-Bradley, a Rockwell Automation business
Copyright © 2002 Delmar Thomson Learning SLC 5/05 Modular Processor Image courtesy of Allen-Bradley, a Rockwell Automation business
Copyright © 2002 Delmar Thomson Learning General Electric Series Series processors come in two configurations: Processor embedded in baseplate Modular processor
Copyright © 2002 Delmar Thomson Learning Model CPU 311 and Model CPU 313 Image courtesy of GE Fanuc Automation
Copyright © 2002 Delmar Thomson Learning GE Series Embedded Processors Image courtesy of GE Fanuc Automation
Copyright © 2002 Delmar Thomson Learning Five-slot Modular CPU Baseplate Image courtesy of GE Fanuc Automation
Copyright © 2002 Delmar Thomson Learning Modular CPU 351 and CPU 363 Image courtesy of GE Fanuc Automation
Copyright © 2002 Delmar Thomson Learning Series Ten-Slot Modular CPU Baseplate Image courtesy of GE Fanuc Automation