Read Input Status (02); Read Output Registers (03); Read Input Registers (04) - Athena C10 Communications Manual

Example: Request for slave 17 to read bits 0004 to 0015.
ADDR
11
Answer
In addition to the address of the slave and the function code (01), the
message comprises a character containing the number of data bytes and
the characters containing data. The data are compacted, so one byte
contains the status of 8 bits, the least significant bit of the first byte must
contain the bit corresponding to the starting address and so on. If the
number of bits to be read is not a multiple of 8, the last character must be
completed with zeros in the most significant bits.
Example: Answer to the request indicated above.
ADDR
11

3.2 Read Input Status (02)

This function works in exactly the same way as the previous one.

3.3 Read Output Registers (03)

This function is used for requesting the value of 16-bit (word) registers
containing numeric variables. Broadcast mode is not allowed.
Question
In addition to the address of the slave and the function code (03), the
message contains the starting address expressed in two bytes and the
number of words to be read, also occupying two bytes. The maximum
number of words that may be read is 125. Address numbering starts from
zero (word1 = 0) for MODBUS, or one (word1 = 1) for JBUS.
Example: Request for slave 25 to read registers 069 to 0071.
ADDR FUNC
19
Answer
In addition to the address of the slave and the function code (03), the
message comprises a character containing the number of data bytes and
the characters containing data. The registers require two bytes each, the
first of which contains the most significant byte.
Example: Answer to the request indicated above.
ADDR FUNC
19 03

3.4 Read Input Registers (04)

This function works in exactly the same way as the previous one.
DATA DATA
FUNC start start
Addr HI Addr LO
01 00 03
DATA DATA
FUNC Byte bit
Count 04..11
01 02 CD
DATA DATA DATA
start start word #
Addr HI Addr LO
03 00 44
DATA DATA DATA DATA
Byte word word word
Count 69 HI 69 LO 70 HI
06 02 2B 00
DATA DATA
bit # bit #
HI LO
00 0C
DATA CRC CRC
bit
12..15 HI LO
0B 6D 68
DATA CRC CRC
word #
HI LO HI
00 03 46
DATA DATA DATA
word word word
70 LO 71 HI 71 LO
00 00 64
CRC CRC
HI LO
CE 9F
LO
06
CRC CRC
HI LO
AF 7A
11