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Working people make mistakes, some people do never make mistakes!
I work to live, my boss thinks I live to work!
In this section I want to explain the internal function SFC 64
"TIME_TCK". I'm using the function to make a replacement for the
internal timer functions. The system time is a "time counter" counting
cyclically from 0 to a maximum of 2147483647 ms (more then 24H). In
case of an overflow the system time is counted again starting with 0.
(this means that all my functions have a problem if the PLC is running
longer then 1 day!! But the most machines run not that long. In that
case you can use the normal functions.)
If you now the internal functions SFB 4 "TON" and SFB 5 "TOF", you
would say WHY? Well using the "Ton" or "Tof" you have to reserve
22 bytes in a DB per timer! My function are using 1 TIME
value (4bytes!). The 400 series has a accuracy of 1ms, the 300serie has
10ms. (But thats enough.)
download awl source (incl. functions.)
Symbol table:
| TIME_TCK | SFC 64 | SFC 64 | Read the System Time. |
| Output (SFC64) | FC 2011 | FC 2011 | Output block FC using SFC 64 as timer |
| Input delay (SFC64) | FC 2012 | FC 2012 | Input on/off delay using SFC 64 as timer |
| Timer ODT (SFC64) | FC 2013 | FC 2013 | Timer using IEC SFC64 |
| Elapsed Time (SFC64) | FC 2014 | FC 2014 | Elapsed Time for TimeValue using SFC64 |
| 8 Input delay (SFC64) | FB 2012 | FB 2012 | 8 on - off delay timer (same in and same out time) |
SFC 64: SFC 64 : Read the System Time.
| Input: | EN | Enable function |
| Output: | RET_VAL | The RET_VAL parameter contains the read system time in the range from 0 to 231-1 ms. |
| ENO | ?? |
FC 2013: FC 2013 : Timer using IEC SFB64.
| Input: | EN | Enable function |
| Input | Start timer. (Current time is stored in TimeValue on positive flank of signal.) | |
| Time_on | The time before ENO becomes high. | |
| In/Output: | TimeValue | See above. Comparing this value with the current time the function determines if the time has elapsed. |
| Output: | ENO | High if time elapsed and the input is high. |
FC 2014: FC 2014 : Elapsed time using timer SFC 64.
| Input: | EN | Enable function |
| TimeValue | Start timer. (Current time is stored in TimeValue on positive flank of signal.) | |
| Output: | Elpased | Comparing this value with the current time the function determines how long the time has elapsed. (Useful for debug or monitor function.) |
| ENO | High if time elapsed and the input is high. |