1. Chapter 10 Advanced Programming, PLC Interfacing, and Troubleshooting

2. Jump Commands
PLCs have instructions that allow the normal sequential execution of the program to be altered if certain conditions exist
Output instructions that perform this function are known as override commands
An example of an override command would be the jump instruction

3. Implementing Jump Instructions
The jump instruction allows the program to skip certain parts of a program, effectively allowing several programs
A set of rung conditions precede the jump instruction. When rung conditions are true, the jump will take place
The jump will be always be associated with a label, which defines the jump to location
Several jump instructions can use the same label as the jump location

4. Jump to Subroutine
Another jump operation is the subroutine operation (JSR)
A JSR label tells the program where to jump to
A return (RET) instruction is used at the end of the subroutine to tell the program to continue executing where it left off

5. Data Manipulation
Data manipulation instructions allow data to be manipulated by shifting bits left or right in a register permitting more efficient programming of the PLC
Shift registers are used for most data manipulation instructions
An example of forward shift registers in an application is demonstrated on the right

6. Programming Implementation of Shift Register Example

7. Shift Register Operations
Bit Shift Left (BSL) will shift data left within a register for each false-true rung transition
Bit Shift Right (BSR) will shift data right within a register for each false-true rung transition

8. Sequencers
Before PLCs, the control of an automatic machine was often performed by a drum sequencer
As the drum rotated, pegs and cams determined what outputs and the dwell of the outputs during a cycle

9. PLC Sequencers
PLCs can perform sequencer functions on entire words within the PLC
The words are transferred from memory to output modules in consecutive order
Parameters necessary for sequencer operations include:
File - designated memory location that forms the 16-bit pattern of the outputs during the sequence
Mask - some bits in a word need not be controlled during a sequence. These bits are masked out
Dest - the output destination to which the data in the sequencer is to be transferred to
Control - this parameter indicates the address of where the control bits of the instruction are located
Length - number of steps of the sequencer file starting at position 1
Position - this parameter shows the actual step in the sequence that’s being performed

10. Architecture of Sequencer Output Instructions

11. Discrete Input/Output Modules
Discreet I/O modules contain the necessary connections and interfacing between field devices and the internal process unit
Many types of I/O modules are available to accommodate different requirements for power, interfacing, and logic

12. Types of Field Devices Connected to I/O Modules

13. Discrete Input Modules
There are two types of field devices that operate in on/off modes:
Relay contacts
Solid-state relays
PLC produce several types of discrete input modules for connection to field devices
Specifications for input modules should take into consideration the following requirements:
Type of current (AC or DC)
Voltage level
Number of inputs
Active-high or Active-low inputs

14. Relay Contact Input Modules

15. Discrete Output Modules
Several types of discrete output modules are available to handle a variety of applications
Requirements for output modules should take into consideration:
AC or DC current
Voltage level
Active-high or Active-low outputs
Relay or Solid-state relay switching
Load capability

16. Types of DC Output Modules
Relay output Solid-state active-high Sinking active-low

17. Troubleshooting I/O Interfaces
Three steps are used to test the proper operation of discrete input interfacing:
Input Testing
Observe indicator light on the PLC module, it should turn off and on in response to the push button
If the light doesn’t turn on, a voltmeter should be used to test the signal at the input terminal
In an improper reading is measured, the next step is to disconnect from the terminal of the module and the power source, then perform a continuity test

18. Troubleshooting Discrete Output Modules
The following steps should be used to troubleshoot output modules:
Activate the output terminal of the module
An indicator lamp connected should energize
If the lamp fails to light and the field device fails to energize, the problem may lie within the program

19. Analog Input and Output Modules
These modules are fed analog signals and then convert them into equivalent digital signals for the PLC to work with.
Analog input modules are sometimes used with sensors and transducers to perform process control functions such as PID control
The most common analog signal used is the 4-20 mA level associated with process control, however other ranges are available or selectable

20. Special Purpose Modules
Several types of special purpose modules are available for a variety of applications, including:
Bar Code modules
Radio Frequency (RF) modules
Vision System modules
PID Control modules
Fuzzy Logic modules
Stepper Motor modules
Thermocouple modules

21. Troubleshooting Programmable Controllers
The most effective approach to troubleshooting PLC faults is to use a logical procedure
Typically, six areas of a PLC are likely to be the source of faults:
I/O field wiring
Incorrect wiring of the field devices
Input module
CPU or power supply
Programming error
Output module