LSIS XGL-C22A, Руководство пользователя, Страница: 154 / 299

Chapter 8 Modbus Communication
8-5
(c) In case of response frame (In case of receiving abnormal frame)
Frame Station no. Error code
Exceptional
code
Tail (CRLF)
Size
(byte)
1 1 1 2
(2) Details of frame
(a) Station no.: indicates the station no. of slave to read bit of output area.
(b) Function code: ‘01’ indicating Read Coil Status
(c) Address: start address of data to read and it consists of 2 byte. At this time, start address conforms to modbus
address regulation.
(d) Data size: size of data to read and it consists of 2 byte.
(e) Frame error check: in case of ASCII mode, it uses LRC and in case of STU mode, it uses CRC. It consists of 2
byte.
(f) Tail: it is applies in case of ASCII mode, CRLF is added after LRC.
(g) No. of byte: no. of byte of response data
(h) Data: makes address of request frame as start address and transmits data with byte unit
(i) Error code: error code is expressed by adding 80(Hex) to function code and in case of reading bit of output area,
it is expressed as 81(Hex).
(j) Exceptional code: indicates detail of error and consists of 1 byte
(3) Frame example
Example that requests reading bit of 20~28 to station number 1 server acting as modbus RTU mode
(a) Request frame
Classification Station no.
Function
code
Address Data size
Error check
Upper byte Lower byte Upper byte Lower byte
Frame 01 01 00 13 00 13 CRC
(b) Response frame (In case receiving normal frame)
Classification Station no.
Function
code
No. of byte Data Error check
Frame 01 01 03 12 31 05 CRC
(c) Response frame (In case of receiving abnormal frame)
Classification Station no. Function code Exceptional code Error check
Frame 01 81 02 CRC