Host Link Communications - Omron CQM1H-SCB41 Operation Manual

Host Link Communications

4-1

Host Link Communications

Host-initiated
Communications
Slave-initiated
Communications
34
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
specified 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 com-
puter.
Host computer
The host sends a command to the PC. The PC processes the command and
returns 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.
Host computer
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 bytes (61 words) of data can be sent. Refer to the CQM1H-series PC Pro-
gramming Manual for details.
TXD(48)
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 10 1 x 10
Node No.
Note If the PC is sending a response to a Host Link command when the TXD( )
instruction is executed, the EX command for TXD( ) will be sent after the
response.
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
specified data is sent without conversion.
Command
Response
ASCII data
S
First source word
C
Control word
Number of bytes: 4 digits BCD, 0000 to 0061
N
0
E X
Send data (ASCII)
Header 122 characters max.
code
Section 4-1
CQM1H-series PC
CQM1H-series PC
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FCS Terminator