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# Chapter 16 timers and counters

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### Transcript

• 1. Chapter 16 Timer and Counter Instructions
• 2. Objectives
• Describe the function of an on-delay timer.
• Describe the function of an off-delay timer.
• Describe in what instances one would use a retentive timer.
• Describe the function of an up counter.
• Describe the function of a down counter.
• Describe in what instances one would use an up counter versus a down counter.
• Define preset, accumulative value, and the timer or counter address.
• Explain how the various timers and counters are reset.
• 3. T4, Timer File
• The timer file stores only timer elements.
• An element is a word or group of words that work together as a unit.
• A timer is made of of three pieces or words.
• Preset value
• Accumulated value
• Status bits
• The preset value and accumulated value are 16-bit signed integers.
• Status bits are single bits that make up one 16-bit word.
• These three words work together as a unit.
• 4. One Timer Element Is Made of Three 16-bit Words
• T4 = timer file 4
• :2 = timer element #2 (0-255 timer elements per file)
• 6. Sub-element
• A sub-element is part of an element addressable as a unit.
• The preset value and accumulated value are sub-elements of a timer.
• T4:0.PRE
• T4:0.ACC
• 7. Timer Status Bits
• Timers have three status bits.
• Done bit (DN) is true when the accumulated value and preset are equal.
• Timer timing bit (TT) is true when the timer is timing.
• Enable bit (EN) is true when the timer instruction is enabled or true.
• Status bit addresses for timer file 4, timer element 2 (T4:2) are listed below:
• T4:2/DN is the address for the done bit.
• T4:2/EN is the address for the enable bit.
• T4:2/TT is the address for the timer timing bit.
• 9. Timer File T4
• 10. C5, Counter File (1 of 2)
• The counter file stores only counter elements.
• An element is a word or group of words that work together as a unit.
• A counter is made of three pieces or words.
• Preset value
• Accumulated value
• Status bits
• 11. C5, Counter File (2 of 2)
• The preset value and accumulated value are 16-bit signed integers.
• Status bits are single bits that make up one 16-bit word.
• These three words work together as a unit.
• 12. One Counter Element Is Made of Three 16-bit Words
• Sample counter element address C5:2
• C5 = timer file 5
• :2 = counter element #2 (0-255 timer elements per file)
• 14. Sub-element
• A sub-element is part of an element addressable as a unit.
• The preset value and accumulated value are sub-elements of a counter.
• C5:0.PRE
• C5:0.ACC
• 15. Counter Status Bits (1 of 2)
• Counters have five status bits.
• Done bit (DN) is true when the accumulated value and preset are equal.
• Count up enable bit (CU) is true when the up counter is true or enabled.
• Count down enable bit (CD) is true when the count down counter is enabled or true.
• 16. Counter Status Bits (2 of 2)
• The overflow bit (OV) is true when the up counter has overflowed above +32767.
• The underflow bit (UN) is true when the down counter has underflowed below -32768.
• The update accumulator bit (UA) is a high-speed counter status bit for fixed SLC 500 PLCs.
• 17. Counter Status Bit Addressing
• Status bit addresses for counter file 5, counter element 0 (C5:0) are listed below:
• C5:0/DN is the address for the done bit.
• C5:0/CU is the address for the count up enable bit.
• C5:0/CD is the address for the count down enable bit.
• C5:0/OV is the address for the count up overflow bit.
• C5:0/UN is the address for the count down underflow bit.
• 18. Counter File C5
• 19. SLC 500 On-delay Timer
• 20. SLC 500 Timer Instructions
• 21. SLC 500 On-delay Timer and Associated Status Bits
• 22. SLC 500 Off-delay Timer
• 23. SLC 500 Retentive Timer
• 24. Retentive Timer and Its Reset Instruction
• 25. SLC 500 Counters
• 26. SLC 500 Count Up Counter
• 27. SLC 500 Count Down Counter
• 28. SLC 500 Count Down Counter Instruction
• 29. Reset Instruction to Reset Counter C20:7
• 30. Using the Clear Instruction to Clear C5:0.ACC and C5:1.ACC