Example 1:
A query about 10 first DMX channels in hexadecimal notation reads
as follows:
00 00 00 00 00 06 00 03 20 00 00 0A
PDU explained:
03 – Modbus function code: 03, meaning “
Read Holding Registers
”
20 00 – address of the register being read – 0x2000 = 8192 – corresponds
to DMX output channels
00 0A – number of registers requested – 0x00A = 10 – DMX channels
Expected response:
00 00 00 00 00 17 00 03 14 00 xx 00 xx 00 xx 00 xx 00 xx 00 xx 00 xx 00 xx 00 xx 00 xx
Except for the “
Lenght
” field, the header is always the same as in the query.
The function code is copied from the query.
14 – 0x14 = 20 – the number of bytes read
00 xx – the values of subsequent DMX channels, where xx is within the range
0x0000 to 0x00FF, meaning from 0 to 255
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