Omron CQM1H-SCB41 operation manual Error Response Frame Format, FCS Frame Check Sequence

Connections Section 4-4

Error Response Frame Format

When the response is longer than 131 characters, it will be divided into more than one frame. A carriage return delimiter (↵ , CHR$(13)) instead of a terminator will automatically be set at the end of the frame. A terminator will be set at the end of the last frame.

Item	Function
@	An “@” symbol is placed at the beginning of every response.
Local Host	The PC’s Host Link node number set in DM 6553 or DM 6558 of
Link Node	the PC Setup.
No.
Header code	The 2-character command code is returned.
End code	The status of command execution is returned (normal end code).
Text	The results of the command are returned.
FCS	The 2-character Frame Check Sequence code is returned.
Terminator	Two characters, “ ” and the carriage return (CHR$(13)) indicate the
	end of the response.

An error response from the PC is returned in the format shown below. Prepare a program at the host so that the response data can be interpreted and processed.

@ x 101 x 100	x 161 x 160			↵
Node No.	Header End code	FCS	Terminator
	code

FCS (Frame Check Sequence)

The header code and text depend on the Host Link command that was received. The end code indicates the completion status of the command (e.g., whether or not an error has occurred).

Item Function

@An “@” symbol is placed at the beginning of every response.

Local Host	The PC’s Host Link node number set in DM 6553 or DM 6558 of
Link Node	the PC Setup.
No.
Header code	The 2-character command code is returned.
End code	The status of command execution is returned (error code).
FCS	The 2-character Frame Check Sequence code is returned.
Terminator	Two characters, “ ” and the carriage return (CHR$(13)) indicate the
	end of the response.

When a frame is transmitted, an FCS code is placed just before the delimiter or terminator in order to check whether an error has occurred in the transmission. The FCS is 8-bit data converted into two ASCII characters. The 8-bit data is the result of an EXCLUSIVE OR performed on the data from the beginning of the frame until the end of the text in that frame (i.e., just before the FCS). Calculating the FCS each time a frame is received and checking the result against the FCS

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