B-16 F650 Digital Bay Controller GE Multilin
B.1 MODBUS PROTOCOL FOR 650 APPENDIX B
B
With this frame the buffer pointer will be set over the 7421 event, which in the example is the oldest one in the buffer, so it
will send back all events until number 7435.
Now, to read the following 15, from 7436 to 7450, it is necessary to calculate the initiation address and send another frame:
Hex(7436)= 0x1D0C
0x1D0C AND 0x00FF= 0xOC
0xFD00+0x0C= 0xFD0C: initiation address
[0xFE 0x03 0xFD 0x0C 0x00 0x69 0x60 0x44] ---------> RELAY
So, it will be asked until the relay responds 0 in one of the events, or reading address 0x03FF and checking the event
number from the last event read.
Second possibility: read directly the memory from the 0xFD00 to 0xFDFF address and then arrange by event number.
From that moment, only the new ones must be requested.
NEW EVENTS
In the 0x03FF address there is the number of the following event that is going to be written, therefore, it is possible to know
how many events must be read from the last time that the relay was asked. If the relay indicated that the new event to be
generated is the 7677.
(NOTE: the 0x03FF address will have the event number 7677, because the last one is 7676).
Supposing that we all events until number 7674 have already been read, now a frame must be sent to read the
corresponding 28 bytes to events 7675 and 7676, given that there are only two new events from the last time that they were
requested.
Hex(7675)=0x1DFB
0x1DFB AND 0xFF=0xFB
0xFD00+0xFB=0xFDFB: reading address (*)
[0xFE 0x03 0xFD 0xFB 0x00 0x0E 0x90 0x5C] ---------> RELAY
Event
Number
7424 7425 .......... 7675 7676 7421 7422 7423
Address 0xFD00 0xFD01 0xFDFB 0xFDFC 0xFDFD 0xFDFE 0xFDFF
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