Controlword/Statusword 2 and Sign of Life (STW2/ZSW2)
Certain telegrams contain an additional 16 bit controlword and statusword. The PROFIdrive profile specifies the use for bits 12-15 for sign-of-life behavior used in IRT, while bits 0-11 are left to the manufacturer and are not used in AKD2G.
| Bit Number | Description | Comment |
|---|---|---|
| 0-12 | Reserved | |
| 12-15 | Master sign of life | A 4 bit counter that increments each cycle. The drive uses this to verify synchronization. See sign-of-life description below. |
| Bit Number | Description | Comment |
|---|---|---|
| 0-11 | Reserved | |
| 11 | Pulses enabled | Indicates when the power stage is enabled or not. This is similar to ZSW1 bit 2 (operation enabled) except this bit is set during certain stopping actions when ZSW1 bit 2 may not be. |
| 12-15 | Drive sign of life | A 4 bit counter that increments each cycle. The master verifies the counter increments are correct for each cycle. See Sign of Life description below. |
Sign of Life
The sign of life functionality in STW2/ZSW2 allows the drive and master to monitor the connection to one another and fault if unsynchronized behavior is detected.
The counter from STW2 is monitored to verify it increments each cycle. In each cycle, the counter is checked against an expected value. If it does not match, an error counter is incremented by 10. If it matches, the error counter is decremented by 1. The error counter cannot be less than 0.
If the error counter is exceeds 10 * max sign of life errors AXIS#.PROFINET.MAXSOLFAIL (P925) then a fault is triggered.
By default the sign of life threshold is set to 1, meaning it tolerates one failure, but if another failure occurs before the error counter decrements back to 0 a fault occurs.
The current error count can be monitored using AXIS#.PROFINET.SOLFAILCNT.
