The L9_XMIT (transmit) function block sends Modbus messages from a master PLC to multiple slave PLCs or sends ASCII character strings from the PLC's Modbus slave port #0 and port #1 for Modicon Momentum platforms and port #1 for Modicon Quantum platforms, to ASCII printers and terminals. L9_XMIT sends these messages over telephone dial up modems, radio modems, or simply direct connection.
L9_XMIT comes with three modes: communication, port status, and conversion.
These modes are described in the following sections.
L9_XMIT performs general ASCII input functions in the communication mode including simple ASCII and terminated ASCII. You may use an additional L9_XMIT function block for reporting port status information into memory words while another L9_XMIT function block performs the ASCII communication function. You may import and export ASCII or binary data into your PLC and convert it into various binary data or ASCII to send to DCE devices based upon the needs of your application.
The function block has built in diagnostics, which helps to ensure no other L9_XMIT function blocks are active in the PLC. Within the L9_XMIT function block a control table allows you to control the communications link between the PLC and Data Communication Equipment (DCE) devices attached to Modbus port #0, port #1, or port#2 of the PLC. The L9_XMIT function block does not activate the port LED when it's transmitting data.
NOTE: The Modbus protocol is a master/slave protocol designed to have only one master when polling multiple slaves. Therefore, when using the L9_XMIT function block in a network with multiple masters, contention resolution and collision avoidance is your responsibility and may easily be addressed through ladder logic programming.
