Communications Procedure - Omron CQM1H - PROGRAM Programming Manual

Communications Procedure

6-3 Communications Procedure
Frame Transmission and Reception
Commands from Host
Frame (command)
Header code
Host
computer
Next frame transmission
enabled (i.e., transmission
right transferred)
PC
Commands from PC
442
Host Link communications are executed by means of an exchange of com-
mands and responses between the host computer and the PC.
With the CQM1H, there are two communications methods that can be used.
One is the normal method, in which commands are issued from the host com-
puter to the PC. The other method allows commands to be issued from the
PC to the host computer.
Commands and responses are exchanged in the order shown in the illustra-
tion below. The block of data transferred in a single transmission is called a
"frame." A single frame is configured of a maximum of 131 characters of data.
The right to send a frame is called the "transmission right." The Unit that has
the transmission right is the one that can send a frame at any given time. The
transmission right is traded back and forth between the host computer and the
PC each time a frame is transmitted. The transmission right is passed from
the transmitting Unit to the receiving Unit when either a terminator (the code
that marks the end of a command or response) or a delimiter (the code that
sets frames apart) is received.
In Host Link communications, the host computer ordinarily has the transmis-
sion right first and initiates the communications. The PC then automatically
sends a response.
Unit no.
Text
FCS
Terminator
Unit no.
Header code
End code
Terminator
Frame (response)
With CQM1H PCs, it is also possible in Host Link communications for the PC
to send commands to the host computer. In this case it is the PC that has the
transmission right and initiates the communications.
Frame (command)
Unit no.
Header code
Text
FCS
Terminator
Text
FCS
Host
computer
Unit no.
Header code
Text
PC
FCS
Terminator
Section 6-3
Unit no.
Header code
End code
Text
FCS
Terminator
Frame (response)
No response