Omron CQM1H-SCB41 operation manual Protocol, Normal Response Frame, Format

Application Procedure Section 4-4

4-4 Host Link Communications

4-4-1 Protocol

Host Link communications are executed by means of an exchange of com- mands and responses between the host computer and the PC. The command or response data that is transferred in one exchange is known as a frame and one frame can contain up to 131 characters of data.

The frame formats for Host Link commands transmitted from the host computer and responses returned from the PC are described below. The PC automatically returns an ASCII-code response when it receives an ASCII-code command from the host computer. The host computer must have a program that controls the transmission and reception of the commands and responses.

Command Frame Format When transmitting a command from the host computer, prepare the command data in the format shown below.

@ x 101 x 100					↵
Node No.	Header	Text	FCS	Terminator
	code

The header code and text depend on the Host Link command being transmitted. When a compound command is transmitted, there will be a second sub-header code.

The FCS (Frame Check Sequence) code is calculated at the host computer and set in the command frame. The FCS calculation is described later in this section.

The command frame may be up to 131 characters long. A command of 132 char- acters or more must be divided into more than one frame. To split the command, use a carriage return delimiter (↵ , CHR$(13)) instead of a terminator. A termina- tor must be used at the end of the last frame.

When dividing commands such as WR, WL, WC, or WD that execute write op- erations, be careful not to divide into separate frames data that is to be written into a single word. You must divide frames so that they coincide with the divisions between words.

Item	Function
@	An “@” symbol must be placed at the beginning of every command.
Destination	Identify the PCs by the Host Link node numbers (0 to 31) set in DM
Node No.	6558 and DM 6553 of the PC Setup.
Header code	Set the 2-character command code.
Text	Set the command parameters.
FCS	Set a 2-character Frame Check Sequence code.
Terminator	Set two characters, “ ” and the carriage return (CHR$(13)) to
	indicate the end of the command.

Normal Response Frame		A normal response from the PC is returned in the format shown below. Prepare a
Format		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	Text	FCS	Terminator
		code

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).

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