B.6.9 Enqueueing Messages - GE Multilin W650 Instruction Manual

APPENDIX B
In ModBus protocol, as in other protocols, exists an internal procedure in message reception and transmission.
When a relay gets a string, determined by a silence of 3 or 4 characters, it is queued in a FIFO queue, for a later processing
in its own protocol. When the protocol is free of execution, it searches in the queue for strings to respond of the FIFO. If
there is such string, it processes it and then it is responded.
Several criteria have been adopted for real time operation:
- Each reading or writing is respond as soon as possible.
- This implies that when settings are changed and respond, a writing request recognition is indicated and then, the
modification of internal settings is performed, (PERFORMING IT IN THE SHORTER TIME WITHOUT PROTECTION),
and finally, settings are stored in a non-volatile memory device.
NOTE: As the relay is internally a modular system, it is possible that the response of some process is slower than what is
expected by the external program, considering the message as missed and sending again another request. If so, there will
be 2 queued messages and therefore, 2 messages will be responded. For this reason, response message 'ACK' must be
verified with its request, and special attention must be paid to setting confirmation writings, especially with reference to
time-out. EnerVista 650 Setup software is recommended to do the configuration modifications, as this software takes into
account all these details.
GEK-113032A W650 Wind Generator Protection System
B.6 EVENTS STATUS REQUEST (ALARMS)

B.6.9 ENQUEUEING MESSAGES

B
B-29