Functions of the IM 178-4
6-5
IM 178-4
C79000-G7076-C178-01
Status bit
SYN_Q
User terminates
synchronization after
detecting SYN_Q=1.
Control bit
SYN
status bit
SYNC
User requests
synchronization
t
t
t
Figure 6-2
Handshaking Between the User Program and IM 178-4 with Software
Synchronization
If synchronization is started using the zero mark, I1, or zero mark and I1, the
IM 178-4 does not monitor the SYN control bit for a rising edge, but for the value
TRUE. If SYN has the value TRUE, then each time the synchronization condition
occurs, the actual position value is reset and marked as synchronized (SYN status
bit has the value TRUE). SYN_Q is not set.
This allows you, for example, to implement a rotary axis with incremental sensors.
6.1.2
Error Monitoring
Startup Tests
During its startup, the IM 178-4 tests the hardware. If a fault is detected, only the
SF LED is lit (see Section 7.1) and the module does not change to normal
operation.
Watchdog
Watchdog timers monitor the module functions. If a timeout occurs, the SF LED is
lit (see Section 7.1) and the module stops normal functions. You can only clear this
status by turning off the 24 V module power supply (1L+) and then turning it on
again.