Rockwell Automation 1734-485ASC POINT I/O ASCII User Manual - Manual (Page 50)

Publication 1734-UM009B-EN-P - July 2003
2-24 Configuring Your ASCII Module
Transmit Handshake vs. Transmit Immediate Mode
This option defines when the ASCII module transmits data out is serial
port. Transmit Handshake mode is used primarily in Polled I/O to
prevent the ASCII module from repeatedly sending its data buffer to
the serial device each time an I/O command is received.
With Transmit Handshake active (default), the Master will change
the TX Transaction ID value in the message header whenever it wants
the ASCII module to send a serial string to the target serial device. The
module monitors the second byte (TX Transaction ID) of the Poll
command or explicit message to determine whether or not the
consumed data from the DeviceNet master is to be transmitted out the
serial port.
The module will not transmit the command data until it receives a
new TX ID value. Upon sensing a change in value of the TX ID byte,
the module transmits the data. It will initiate one serial transmission
for each change in the TX ID value, regardless of the data string value.
In Transmit Immediate mode, the ASCII module ignores the TX ID
byte value and initiates a new serial port transmission with each
message received from DeviceNet. This technique can be useful when
the target ASCII device is not affected by receiving the same data
multiple times and operates quickly enough so that message
overflows do not occur. This option may be most useful with explicit
messages.
These actions take place with either a Poll command or an explicit
message that writes to the consume assembly object or the serial port
object.