z28z34man (Customer) asked a question.
when in the scan order is the tag database updated from a network read instruction and when in the scan order in remote project is the tag database updated from a network write instruction? the manual says updated immediately but what is meant by immediately. i woulddn't expect the network read instruction to be a blocking instruction and waiting for a response there as network issues could cause watch dog faults.
this is what is in the manual
Note: Tag Values are updated immediately as each Ladder Rung is executed, top to bottom. However, Tag Values representing physical Outputs are only applied to the physical Output after the END statement of the last Task to be scanned is reached. Outputs in Remote Base Groups have additional limitations regarding Update Intervals.
Write Operations:
When a write instruction is executed, the data is read directly from the tags at the moment the instruction runs. This means the data is captured mid-scan, inline with the ladder logic execution.
Read Operations:
For read operations, tag values are updated when the Modbus response is received. Because the CPU processes incoming Ethernet packets (Modbus messages) at the end of the scan cycle, tag updates occur after the ladder logic has finished executing — outside of the ladder logic itself.
In summary, write data reflects tag values at the point of instruction execution, while read data reflects tag values as of the end of the previous scan cycle.