IMO Precision Controls K7 Series User Manual page 192

Chapter 8 Communication Function
3) Address area
(1) Setting range is available from 1to 247, but K7 supports from 0 to 31.
(2) Address 0 is used for broadcast address. Broadcast address is all slave device recognize and respond to like
the self-address, which can't be supported by MK80S.
4) Function code area
(1) K7 supports only 01, 02, 03, 04, 05, 06, 15, and 16 among Modicon products' function codes.
(2) If the response format is confirm+(ACK), it uses the same function code.
(3) If the response format is confirm-(NCK), it returns as it sets the 8th bit of function code as 1.
Ex) If function code is 03, (we write here only function code part. Because only function codes are different.)
[Request ]
[Confirm+]
[Confirm-]
5) Data area
(1) It sends data, using ASCII data(ASCII mode) or hex (RTU mode).
(2) Data is changed according to each function code.
(3) Response frame uses data area as response data or error code.
6) LRC Check/CRC Check area
(1) LRC (Longitudinal Redundancy Check) : It works in ASCII mode. It takes 2 ' complement from sum of frame
except header or tail to change into ASCII code,
(2) CRC (Cyclical Redundancy Check): It works in RTU mode. It uses 2-byte CRC check rules.
REMARK
1) All numerical data can use hexadecimal, decimal, and binary type. If we convert decimal 7 and 10 into each type:
Hexadecimal : H07, H0A or 16#07, 16#0A
Decimal : 7, 10
Binary : 2#0111, 2#1010
0000 0011 (H03)
0000 0011 (H03)
1000 0011 (H83)
8-69
It returns as it sets the 8th bit of
function code of request frame.