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Chapter 2 Built-in Cnet communication
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When receiving the abnormal frame from client, server transmits error code and exceptional code. Error code is
function code adding 80(Hex) and exceptional code indicate the specific error content. Each code has following
content.
Code Code name Meaning
01 Function code error Function code error
02 Address error Exceeds allowed address range
03 Data setting error Not allowed data value
04 Server error Server(slave) is error
05
Server requesting
re-transmission
Now server is too busy to process and requests re-transmission later
06
Server process time
delay
Server takes time to process. Master should request again.
2.7.2 Frame Structure
1) Frame structure in ASCII mode
Frame structure in the ASCII mode is as follows.
Classification Start Station no. Function code Data Error check End
Size (byte) 1 2 2 N 2 2
(1) Characteristic of ASCII mode
a) In the ASCII mode, start of frame is indicated with colon (:), which is ASCII code, and end of frame is indicated
with ‘CRLF’.
b) Each character allows maximum 1s interval.
c) How to check the error uses LRC, it takes 2’s complement except frame of start and end and converts it as ASCII
conversion.
(2) Address area
a) It consists of 2 byte.
b) When using the XGT Cnet I/F module, range of station is 0~31.
c) Station number 0 is used for client.
d) When server responds, it contains self address to response frame to know client’s response.
(3) Data area
a) Transmits the data by using the ASCII data, data structure changes according to function code.
b) In case of receiving normal frame, it responds as normal response.
c) In case of receiving abnormal frame, it responds by using error code.
(4) Error check area
How to check error of frame takes 2’s complement except start and end of frame and converts it as ASCII.