Datakom DPR-400 - Data Formats

DPR-400 User Manual Rev_01 Firmware V-1.0
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16-bit variables: These variables are stored in a single register. Bit_0 is the least significant bit (LSB)
and Bit_15 is the most significant bit (MSB).
32-bit variables: These variables are stored in 2 consecutive registers. The 16 least significant bits are
located in the first register and the 16 most significant bits are located in the second register.
Bit arrays: Arrays larger than 16 bits are stored in multiple registers. The LSB of the first register is bit_0.
The MSB of the first register is bit_15. The LSB of the second register is bit_16. The MSB of the second
register is bit_31, and so on.
Record reading is performed using function code 03 (read multiple registers). The MODBUS master
device sends a query. The response can be either the required data or an error message. Up to 123
registers can be read at once. If a query for more than 123 registers is made, an error message is sent as
a reply. Message structure is as follows.
BYTE
DESCRIPTION
VALUE
0
Device Address
1-253
1
Function Code
3
2
Starting
Address (Top)
Detailed explanation given below
3
Starting
Address
(Bottom)
Detailed explanation given below
4
Number of
Registers (Top)
0
5
Number of
Registers
(Bottom)
Max 7Bh (123 decimal)
6
CRC Bottom
Byte
CRC calculation is explained below in detail
7
CRC Top Byte
CRC calculation is explained below in detail
14.3. DATA FORMATS
14.4. READING DATA