Enqueueing Messages; Traces And Troubleshooting - GE Multilin F650 Instruction Manual

B.1 MODBUS PROTOCOL FOR 650
B.1.6.9 ENQUEUEING MESSAGES
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
B account all these details.
B.1.6.10 TRACES AND TROUBLESHOOTING
The tracer is a debugging tool to view the strings in any writing or reading process in ModBus. This tracer is activated in the
menu from F650: View, Traces.
With this option enabled, request and response strings will be shown. If, for instance, request and response strings view is
desired, between F650 and the relay, in general settings reading we will do what follows:
1º. - Activate traces, from View, Traces menu
2º. - Open the general settings menu
The screen will display that group settings, on the left side bottom the relay reading request will appear
<0001><06/18/03 12:14:15>[0xFE 0x03 0x21 0x8A 0x00 0x16 0xFB 0xDD]
And on the right the settings response will appear:
0001><06/18/03 12:14:15>[0xFE 0x03 0x2C 0x3F 0x80 0x00 0x00 0x3F 0x80 0x00 0x00 0x3F 0x80 0x00 0x00 0x3F
0x80 0x00 0x00 0x00 0x00 0x42 0xC8 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x01 0x00 0xFE
0x00 0xFE 0x00 0x06 0x00 0x06 0x00 0x00 0x01 0xF6 0xAC 0xB5]
This way, any request or mechanism to obtain information from the relay, can be viewed string by string.
There is another tool for tracing the relay memory: in F650 menu: Communication, Troubleshooting, any reading to any
address can be requested, the PC will form the string together with check-sum register.
B-20 F650 Digital Bay Controller
APPENDIX B
GE Multilin