Siemens SIMATIC S5 Manual page 93

2 Engineering
Test and diagnostics of communication in the SIMATIC S5
To monitor the FETCH and WRITE functions in the SIMATIC S5-CPU, call the
watch table "BB4" in STEP 5.
The count value (4) is cyclically written in the S7-1500 CPU every second and the
mirrored incremented value is read back via the FETCH connection (1).
The communication and connection status of the FETCH (2) and WRITE functions
(3) can be evaluated via the indicator words (ANZW) of the HTBs.
Ethernet Communication (ISO on TCP) between SIMATIC S5 and
SIMATIC S7-1500 Controllers
Entry-ID: 109482475, V1.2, 07/2019
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