1. Memory Layout and SLC500 System Addresses

2. Processor Memory Division An SLC 500 processor's memory is divided into two storage areas. Like two drawers in a filing cabinet, one area is for data files and the other for program files. Processor memory division and file capacity are shown in the following graphic

3. Processor Memory Organization

4. Program Files Program files contain processor information, the main ladder program, and other ladder files. Program files contain processor information, the main ladder program, and other ladder files. An SLC 500 processor can contain up to 256 program files. An SLC 500 processor can contain up to 256 program files. Program files are located in the Program Files folder of the RSLogix 500 project tree. Program files are located in the Program Files folder of the RSLogix 500 project tree.

5. Program Files

6. Program files are assigned as follows: Program files are assigned as follows: File 0 always contains system information. File 0 always contains system information. File 1 is reserved. File 1 is reserved. File 2 contains the main ladder file. File 2 contains the main ladder file. File 3-255 contains other ladder files (subroutines). File 3-255 contains other ladder files (subroutines).

7. Data Files Data files contain the status information associated with external I/O and all other instructions used in the main and subroutine ladder program files. Data files contain the status information associated with external I/O and all other instructions used in the main and subroutine ladder program files. Data files are located in the Data Files folder of the RSLogix 500 project tree. Data files are located in the Data Files folder of the RSLogix 500 project tree.

8. Data Files

9. Data file organization for SLC-500 controller. The data file portion of memory stores input and output status, processor status, the status of various bits and numerical data. Data Files

10. Input Table File Operation Input module Switch Open Binary 0 stored 0

11. Input Table File Operation Input module Switch Closed Processor continually reads current input status and updates input image table file Binary 1 stored 1

12. Output Table File Operation Output module Output OFF Processor continually activates or deactivates output status according to output image table \file status Status 0 0

13. Output Table File Operation Output module Processor continually activates or deactivates output status according to output image table file status Output ON 1 Status 1

14. SLC 500 Software and Hardware Addressing

15. SLC 500 Processor Data Storage Units The SLC 500 processor stores data in the following units of memory: Bit: A digit in the binary radix (0 or 1). A bit may represent the state, on or off, of a discrete I/O device. Bit: A digit in the binary radix (0 or 1). A bit may represent the state, on or off, of a discrete I/O device. Word: A sequence of 16 bits that is treated as a unit. For example, the 16 bits representing the 16 points of an I/O module comprise one word. Word: A sequence of 16 bits that is treated as a unit. For example, the 16 bits representing the 16 points of an I/O module comprise one word. Element: A word or group of words that work together as a unit. Element: A word or group of words that work together as a unit. Sub-element: Individual words within an element. Sub-element: Individual words within an element.

16. SLC 500 Hardware Address Characteristics The address for a real-world device (input or output) is directly determined by the module slot number and terminal to which the hardware device is wired. The address for a real-world device (input or output) is directly determined by the module slot number and terminal to which the hardware device is wired. Slot numbers are assigned from left to right, beginning with 0. The SLC 500 processor is in slot 0. Slot numbers are assigned from left to right, beginning with 0. The SLC 500 processor is in slot 0. A hardware address contains the following information: A hardware address contains the following information: The module type, either an input (I) or an output (O) module The module type, either an input (I) or an output (O) module The slot number (numbered in decimal from 1 to 30) The slot number (numbered in decimal from 1 to 30) The terminal number (numbered in decimal from 0 to 15) The terminal number (numbered in decimal from 0 to 15)

17. SLC 500 Hardware Address Characteristics

18. SLC 500 Output addressing O:5/0 means that it is a physical output. O:5/0 means that it uses Slot 5 (the 6th physical slot) in the rack. O:5/0 means that it is the first output on the card.

19. SLC 500 Input addressing I:4/0 means that it is a physical input. I:4/0 means that it uses Slot 4 (the 5th slot in the rack). I:4/0 means that it is the first input on the card.

20. Internal Coil Addressing B3:0/0 means that it references an internal Binary file B3:0/0 means that it uses the first word in the table B3:0/0 means that it is the first bit in the word.

21. An example of an SLC 500 I/O address is shown in the following graphic

22. Internal Coil Addressing

23. SLC 500 Input addressing

24. SLC 500 Output addressing

25. SLC 500 Input addressing

26. SLC 500 Output addressing

27. Program Scan During each operating cycle, the processor reads all inputs, takes these values, and energizes or de-energizes the outputs according to the user program. This process is known as a scan. I/O scan – records status data of input devices. Energizes output devices that have their associated status bits set to ON (1) Program scan – instructions are executed sequentially Because the inputs can change at any time, the PLC must carry on this process continuously.

28. Scan Process The scan time indicates how fast the controller can react to changes in inputs. Scan times vary with computer model and program content, and length. If a controller has to react to an input signal that changes states twice during the scan time, it is is possible that the PLC will never be able to detect this change. Scan time may be a concern in high speed operations

29. Scan Process Adjusts outputs Read inputs The scan is a a continuous and sequential process Run program

30. Data Flow Overview Examine data Return results Input modules Output modules Input data Output data Program Check/compare/examine specific conditions Take some action Input image table file Output image table file Lecture – PLC Programming Basics MME 486 – Fall 2006 16 of 62

31. When the input is closed, the input module senses a voltage and an ON condition (1) is entered into the input table bit I:3/6 Input device I:3/6 Input Module During the program scan the processor sets instructions I:3/6 and O:4/7 to ON (1) Scan Process I:3/6 Input file I:3/6 O:4/7 Program Output file O:4/7 The processor turns light output O:4/7 ON during the next I/O scan Output Module O:4/7 Output device

32. Scan Patterns End of ladder Horizontal Scanning Order The processor examines input and output instructions from the first command, top left in the program, horizontally, rung by rung. In addition to the program itself, the scan time is also dependent on the clock frequency of the processor!

33. PLC Programming Languages The term PLC programming language refers to the method by which the user communicates information to the PLC. The three most common language structures are: ladder diagram language, Boolean language, and functional chart. Ladder diagram language Functional chart Boolean language

34. Comparing Programming Language PB1 CR1 CR2 LS1 SOL Relay Schematic PB1 CR1 CR2 SOL LS1 Equivalent ladder diagram language Equivalent Boolean language

35. Relay-Type Instructions The ladder diagram language is basically a symbolic set of instructions used to create the controller program. These ladder instructions symbols are arranged to obtain the desired control logic.

36. Examine If Closed (XIC) Instruction Symbol Analogous to the normally open relay contact. For this instruction we ask the processor to EXAMINE IF (the contact is) CLOSED or ON (XIC) Typically represents any input. Can be a switch or pushbutton, a contact from a connected output, or a contact from an internal output. Has a bit-level address which is examined for an ON condition. The status bit will be either 1 (ON) or 0 (OFF).

37. Examine If Open (XIO) Instruction Symbol Analogous to the normally closed relay contact. For this instruction we ask the processor to EXAMINE IF (the contact is) OPEN (XIO). Typically represents any input. Can be a switch or pushbutton, a contact from a connected output, or a contact from an internal output. Has a bit-level address which is examined for an OFF condition. The status bit will be either 1 (ON) or 0 (OFF).

38. Output Energize (OTE) Instruction Symbol Analogous to the relay coil. The processor makes this instruction true (analogous to energizing a coil) when there is path of true XIC and XIO instructions in the rung. Typically represents any output that is controlled by some combination of input logic. Can be a connected device or an internal output (internal relay). If any left-to-right path of input conditions is TRUE, the output is energized (turned ON).

39. User-programmed rung Closed input Address input terminal I1:3/12 Allen-Bradley SLC-500 Controller Addressing I1:3 12 Output image table file 0 I:3/12 Bit address O:0:4/6 it address Input image table file 1 O:4 6 Energized output Address output terminal O0:4/6

40. PLC Matrix Limitation Diagram There may be limitations to the number of series contacts instructions, number of parallel lines, and the number of outputs and their location on the rung. Max parallel lines Max series contacts No. outputs per rung and location of the output in the rung

41. Extending the Number of Series Contacts Using an Internal Control Relay Internal relay coil Discrete output (requires one physical connection on the output module) Internal relay contact Rung 1 Rung 2

42. A nested branch starts or ends within another branch. Input and output branches can be nested to avoid redundant instructions and to speed up the processor scan time. Nested Input and Output Branches

43. Nested Contact Program A B C Y Nested contact D E On some PLC models, the programming of a nested branch circuit cannot be done directly. A B C D C E Y Contact instruction C repeated Reprogrammed to obtain the required logic.

44. A nested branch starts or ends within another branch. Input and output branches can be nested to avoid redundant instructions and to speed up the processor scan time. Nested Input and Output Branches

45. Nested Contact Program A B C Y Nested contact D E On some PLC models, the programming of a nested branch circuit cannot be done directly. A B C D C E Y Contact instruction C repeated Reprogrammed to obtain the required logic.