The FBD Message block separates command detection from parameter reception. Use the block-level Sync output to detect a configured SMS command, each parameter-level Sync output to detect reception of that parameter, and the corresponding Value output to read its stored value.
Sync pulse duration
Each Sync indication remains active for one program cycle. Logic that must retain the event beyond that cycle must latch or otherwise store the indication within the application.
Block and parameter Sync behavior
| Output | Activation condition | Duration |
|---|---|---|
Block Sync
|
The configured SMS command is received. | One program cycle |
Parameter Sync
|
That parameter is received. | One program cycle |
Do not treat the block-level indication as proof that every parameter was received. Evaluate the individual parameter Sync output when downstream logic depends on a specific value.
Value retention and startup state
A received parameter remains continuously available at its Value output until another value replaces it. On power-up, the output value is zero; therefore, zero can mean either the startup state or a received value of zero unless the application records a parameter Sync event.
- Use the block
Syncoutput when logic only needs to detect the command. - Use the parameter
Syncoutput when logic must confirm that a particular parameter arrived. - Read or copy
Valuewhen the parameterSyncpulse occurs if the application must distinguish received data from the power-up value.
FAQ
How long does the FBD Message block Sync output stay on?
It stays active for one program cycle. Add application logic to retain the event if it must be used later.
When does the block-level Sync differ from parameter Sync?
Block-level Sync indicates receipt of the configured command, while a parameter-level Sync indicates receipt of that specific parameter.
How long does the Message block Value output retain data?
The received value remains at Value until it is replaced. After power-up, Value is zero.
