| Post 1 made on Thursday July 16, 2009 at 17:06 |
danieljgor Long Time Member |
Joined:
Posts: | December 2008
105 |
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Hi Guy's,
I am a first time user of Rs-232. I have a 9600 & serial extender. I would like to control Ness/Everfocus Security DVR via RS232. The info I have so far is:
OPcode =0x4b
0x00 = Channel 1
0x01 = Channel 2
0x02 = Channel 3
0x03 = Channel 4
0X0B = play
Example for play
0x85 (length)
0x7f (Receiver id high byte)
0x7f (Receiver id low byte)
0x4B (Opcode)
0x0B (code for play)
0X59 (checksum)
Any help would be much appreciated
Thanks heaps
Daniel
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| Post 2 made on Wednesday July 22, 2009 at 09:45 |
HiFidel Long Time Member |
Joined:
Posts: | July 2005
165 |
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Is there any info on how that checksum is calculated?
One thing you could try is subtracting from the opcode to get a channel command, and then adding the same amount to the checksum:
0x85 (length)
0x7f (Receiver id high byte)
0x7f (Receiver id low byte)
0x4B (Opcode)
0x02 (code for Channel 3, 0x0B - 0x09)
0X62 (checksum 0x59 + 0x09)
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| Post 3 made on Friday July 24, 2009 at 08:17 |
The checksum is calculated by adding together all the preceeding bytes, discarding anything over 1 byte, then ORing together with 7F.
So for the play example:
0x85 +
0x7f +
0x7f +
0x4B +
0x0B
=======
0x1D9
Discarding anything over 1 byte gives 0xD9, then
0xD9 OR 0x7F = 0x59.
daniel, was it the checksum you were having problems with, or something else?
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