Omron CQM1H-SCB41 operation manual Host Link Communications, TXD-- Instruction

Connections Section 4-1

4-1 Host Link Communications

Host-initiated Communications

Slave-initiated Communications

A Host Link System can be used to send C-mode Host Link commands from a host (e.g., personal computer or PT) to a PC to read/write I/O memory, control operating modes, etc. The PC can also use the TXD(––) instruction to send spe- cified I/O memory data to the host for slave-initiated communications.

Refer to the CQM1H-series PC Programming Manual for details on C-mode commands.

Communications in a Host Link System are normally started by a host computer.

Command

Host computer CQM1H-series PC

Response

The host sends a command to the PC. The PC processes the command and re- turns a response to the host computer. This process is repeated, allowing the host computer to monitor and control PC operation.

The PC can also initiate communications with the host to send data, as may be necessary when errors occur on the line controlled by the PC or to confirm the operating status of the host.

ASCII data

Host computer CQM1H-series PC

When the TXD(––) instruction is executed in the ladder program of the PC, the contents of the I/O memory words specified for the instruction is converted to ASCII and sent to the host. There is no response to this transmission.

TXD(––) Instruction

TXD(48) reads N bytes of data beginning from words S, converts it to ASCII, and outputs the data from the specified port as a Host Link command. Up to 122 by- tes (61 words) of data can be sent. Refer to the CQM1H-series PC Programming Manual for details.

TXD(48)
S	First source word
C	Control word
N	Number of bytes: 4 digits BCD, 0000 to 0061

The format of the Host Link command generated by TXD(––) is shown below. The command header code is EX and is followed by the specified data con- verted to ASCII. There is no response to the EX command.

@ x 101 x 100	E	X	Send data (ASCII)		:	↵
Node No.	Header		122 characters max.	FCS	Terminator
	code

Note If the PC is sending a response to a Host Link command when the TXD(––) in- struction is executed, the EX command for TXD(––) will be sent after the re- sponse.

If TXD(––) is executed in Host Link Mode, the specified data is converted to ASCII before being sent. If TXD(––) is executed in No-protocol Mode, the speci- fied data is sent without conversion.

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