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Read Numeric Variables (FC=03)

Request

This command is requesting the contents of numeric variable # 7021
from the slave device with address 17.

11 03 1B6D 0001 11A3

11: The Slave Address (11 hex = address17 )
03: The Function Code (read Numeric variables)
1B6D: The Data Address of the first variable requested. ( 1B6D hex = 7021 )
0001: The total number of variables requested. (read 1 variable) 
11A3: The CRC (cyclic redundancy check) for error checking.

Response

11 03 04 476C4A00 083B

11: The Slave Address (11 hex = address17 )
03: The Function Code (read Numeric variables)
04 The number of data bytes to follow (1 registers x 4 bytes each = 4 bytes)
476C4A00: The contents of  32-bit variable # 7021
083B: The CRC (cyclic redundancy check).

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