ASCII Configuration – ASCII Message Triggering Method
This method allows the other protocol to signal when to send the next message using data handshakes.
These “signals” are controlled using data variables in the memory manager.
NOTE
: These two data variables will need to be added manually to the Data Mapping webpage since it
will not be mapped using Auto-Map. They are mapped just like the Status_XY variable described in the
Data Mapping- Adding Diagnostic Information section of this user guide.
While these two data variables are mapped, the Change-of-State method is disabled but messages can
still be sent via the Cyclic method, if configured. For more information on the ASCII Triggering Methods,
please see the
Transmit Data – Triggering Methods
section of this user guide.
How the triggering method works:
The mating protocol sends a numbered value to the ASCII TransTrigger diagnostic variable. This
value must be different from the previous value for a new message to be triggered.
Depending on the TransTrigger value, one of 4 things will occur:
1)
If TransTrigger = 65535, then the triggering method is disabled.
2)
If TransTrigger = 0, then the triggering method is enabled, but no message will transmit.
3)
If TransTrigger is between 1-65534
AND
the value
IS
equal to the TransHandshake
diagnostic variable, then no new message will transmit.
4)
If TransTrigger is between 1-65534
AND
the value
IS NOT
equal to the TransHandshake
diagnostic variable, then a new message will transmitted. The value in TransTrigger will then
be moved to TransHandshake.
The value of TransHandshake could be mapped back to the mating protocol for monitoring
purposes.
Example
: For the above example the other protocol in the gateway is the Allen-Bradley PLC. As you can
see from the picture above, the TransTrigger for ASCII Device 1 is mapped to the PLC tag called
Trigger_Tag. If the value in Trigger_Tag is between 1-65534 AND is a different value that is currently
stored in TransHandshake, then a new message will be transmitted to the ASCII device, the value of
TransTrigger will be copied to TransHandshake, and the value of TransHandshake will be written to the
PLC tag, Receive_tag.
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