Omron CPM1 - PROGRAMING MANUAL 02-2001 Programming Manual page 256

CPM2A/CPM2C Communications Functions
Frame Transmission and Reception
Frame (command)
Header code
Host
computer
Next frame transmission
enabled (i.e., transmission
right transferred)
CPM2A/CPM2C
Slave-initiated
Communications
236
In Host Link communications, the host computer ordinarily has the transmission
right first and initiates the communications. The CPM2A/CPM2C then automati-
cally sends a response.
Commands and responses are exchanged in the order shown in the illustration
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 transmis-
sion 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 CPM2A/
CPM2C 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.
Unit no.
Text
FCS
Terminator
Unit no.
Header code
End code
Text
FCS
Terminator
Frame (response)
Data transmissions from the PC to the host computer can be initiated by the CPU
Unit using TXD(48).
Host
computer
CPM2A/CPM2C
Frame (command)
Unit no.
Header code
Text
FCS
Terminator
Unit no.
Header code
Text
FCS
Terminator
Frame (response)
Section
Unit no.
Header code
End code
Text
FCS
Terminator
Frame (response)
There is no response
from the host computer
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