ECT 464
This lecture covers special functions in SLC500 programmable logic controllers, focusing on One-Shot functions like One-Shot Rising (OSR) and One-Shot Falling (OSF), which trigger events on specific input transitions. Key topics include limitations on usage in rungs, labels (LBL), and Jump (JMP) instructions for code flow control, as well as Master Control Reset (MCR) for managing program execution zones. Discussions on subroutines (SBR), Immediate Input/Output with Masks (IIM/IOM), and Temporary End (TND) for debugging highlight advanced control techniques in PLC programming.
ECT 464
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Presentation Transcript
ECT 464 Lecture 4b Special Functions
Special Functions • One Shot (ONS) (OSR) SLC500 • triggers a one time event • activates on false to true transition • rung must go false again to reset • allowed to use one OSR per output in a rung • do not place input conditions after the OSR • uses a bit location to store last state
Special Functions • One Shot Rising (OSR) • triggers a one time event • activates on false to true transition • rung must go false again to reset • allowed to use one OSR per output in a rung • do not place input conditions after the OSR • uses a bit location to store last state • Activates output bit
Special Functions • One Shot Falling (OSF) • triggers a one time event • activates on true to false transition • rung must go true again to reset • allowed to use one OSF per output in a rung • do not place input conditions after the OSF • uses a bit location to store last state • Activates output bit
Special Functions • Label (LBL) • Target of jump instruction • Must be first instruction of rung • 256 labels in each subroutine (SLC) • 1000 labels in each subroutine (M1000)
Special Functions • Master Control Reset (MCR) • Acts on rungs between start and end fence • When off, ignores inputs, and de-energizes all outputs in the zone • When on, inputs and outputs treated normally • Latches, retentive timers, and counters remain in their last state • Must end zone with unconditional MCR • Cannot nest MCR’s • Always place MCR as last instruction on rung
Special Functions • Jump (JMP) • When true, skips to the rung with the LBL instruction and continues executing • When false, doesn’t do anything • Can jump forward and backward • Can jump to the same label from several JMP instructions • Do not jump into a MCR zone • Not between program files
Special Functions • Temporary End (TND) • Stops processor from scanning the rest of the rungs • Used to debug a program • Used to stop the execution of part of a main program or subroutine
Special Functions • Suspend (SUS) • Sends PLC into idle mode • All outputs de-energized • Used with Suspend ID number
Special Functions • Subroutine (SBR) • Marks the beginning of a file • Optional use
Special Functions • Jump to Subroutine (JSR) • Used to execute a subroutine and then return • Saves memory • Nest 8 levels deep • File number 3-255 (SLC or M1500) • File number 4-15 (M1000)
Special Functions • Return (RET) • Marks the end of a subroutine • Can be conditional (SLC) • Optional Use (END works as well) • Can return a value (SLC)
Special Functions • End (END) • Marks the end of a file
Special Functions • Immediate Input with Mask (IIM) • Update data prior to normal scan • Mask of 1 passes • Specify input word • Embedded I/O only
Special Functions • Immediate Output with Mask (IOM) • Update outputs prior to normal scan • Mask of 1 passes • Specify output word • Embedded I/O only
Special Functions • I/O Refresh (REF) • Executes a new I/O scan in middle of execution • Can also do communications
Next Class • I/O Scans and memory layout • PLC Modes
