1. Copyright © 2002 Delmar Thomson Learning Chapter 10 PLC Processors

2. Copyright © 2002 Delmar Thomson Learning Objectives  Describe the function of the processor.  Describe processor operating modes.  Explain the function of the watchdog timer.

3. 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.

4. 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.

5. 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.

6. 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.

7. 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.

8. 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.

9. 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.

10. 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.

11. 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.

12. 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

13. Copyright © 2002 Delmar Thomson Learning Straight Through Cabling between Computer and Peripheral Equipment

14. 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.

15. 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.

16. Copyright © 2002 Delmar Thomson Learning Connecting Two Computers with a Straight Through Cable

17. 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.

18. Copyright © 2002 Delmar Thomson Learning Null-Modem Cable Crosses Pin 2 to Pin 3

19. Copyright © 2002 Delmar Thomson Learning PLC Processors Have Multiple Operating Modes  Processor has two modes of operation:  Program mode  Some variation of run mode

20. 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.

21. 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.

22. 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.

23. 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.

24. 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.

25. Copyright © 2002 Delmar Thomson Learning Processor Communications  The physical connection between a processor and the outside world is called a communication port.

26. 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

27. 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

28. Copyright © 2002 Delmar Thomson Learning SLC 5/03 and 5/04 Communication Ports Image courtesy of Allen-Bradley, a Rockwell Automation business

29. Copyright © 2002 Delmar Thomson Learning Processor Capabilities  A processor’s capabilities are determined by  Memory size  Instruction set  I/O supported  Communication ports

30. Copyright © 2002 Delmar Thomson Learning SLC 5/01 Processor Specifications Image courtesy of Allen-Bradley, a Rockwell Automation business

31. Copyright © 2002 Delmar Thomson Learning SLC 5/02 Processor Specifications Image courtesy of Allen-Bradley, a Rockwell Automation business

32. Copyright © 2002 Delmar Thomson Learning SLC 5/02 Processor Image courtesy of Allen-Bradley, a Rockwell Automation business

33. Copyright © 2002 Delmar Thomson Learning SLC 5/03 Processor Image courtesy of Allen-Bradley, a Rockwell Automation business

34. Copyright © 2002 Delmar Thomson Learning SLC 5/04 Specifications Image courtesy of Allen-Bradley, a Rockwell Automation business

35. Copyright © 2002 Delmar Thomson Learning SLC 5/04 Processor Image courtesy of Allen-Bradley, a Rockwell Automation business

36. Copyright © 2002 Delmar Thomson Learning SLC 5/05 Processor Specifications Image courtesy of Allen-Bradley, a Rockwell Automation business

37. Copyright © 2002 Delmar Thomson Learning SLC 5/05 Modular Processor Image courtesy of Allen-Bradley, a Rockwell Automation business

38. Copyright © 2002 Delmar Thomson Learning General Electric Series 90-30  Series 90-30 processors come in two configurations:  Processor embedded in baseplate  Modular processor

39. Copyright © 2002 Delmar Thomson Learning Model CPU 311 and Model CPU 313 Image courtesy of GE Fanuc Automation

40. Copyright © 2002 Delmar Thomson Learning GE Series 90-30 Embedded Processors Image courtesy of GE Fanuc Automation

41. Copyright © 2002 Delmar Thomson Learning Five-slot Modular CPU Baseplate Image courtesy of GE Fanuc Automation

42. Copyright © 2002 Delmar Thomson Learning Modular CPU 351 and CPU 363 Image courtesy of GE Fanuc Automation

43. Copyright © 2002 Delmar Thomson Learning Series 90-30 Ten-Slot Modular CPU Baseplate Image courtesy of GE Fanuc Automation