Function Description; Operating Modes For Serial Transmission; Transmit Data; Continuous Transmission - WAGO 750-652 Manual

WAGO-I/O-SYSTEM 750
750-652 Serial Interface RS-232 / RS-485
5

Function Description

5.1

Operating Modes for Serial Transmission

In den In the operating modes for serial transmission, the I/O module allows
communication with serial devices via RS-232, RS-485, RS-422 or DMX.
The I/O module operates in these modes as a link between one of these
standardized interfaces to the one side and the application or controller to the
other side.
Data transmission between the I/O module and serial devices is determined by the
respective interface parameters, e.g. baud rate.
Data transmission between the application and I/O module is controlled by the
control and status bytes.
5.1.1

Transmit Data

If data is transmitted via the I/O module to an RS-232, RS-485, RS-422 interface
or in DMX mode, the application writes to the data bytes of the process image
(output) per each part of the data. The application modifies the control bytes, so
that they signal to the I/O module that new data has arrived. The I/O module
receives the data sent to the output buffer and modifies the status bytes. Based on
these modified status bytes, the application can again recognize that the data
transfer was successful. Only when this feedback is present can the application
transmit the next part of the data.
The data transmission rates between the application and I/O module and between
the I/O module and serial interface are normally not identical.
If data transmission between the application and I/O module is faster than
between the I/O module and serial interface, the output buffer in the I/O module
fills up faster than it clears. If the application transmits continuously, the output
buffer queue even rises when data is continuously transmitted on the serial
interface. If the output buffer is full, the application has to wait for space to be
available in the output buffer by transmitting to the serial interface.
If data transmission between application and I/O module is slower than between
I/O module and serial interface, the output buffer in the I/O module fills up faster
than it clears. Transmission of data on the serial interface is repeatedly interrupted
even if the application continuously transmits.
5.1.1.1

Continuous Transmission

The I/O module can be set either to transmit data in the output buffer to the serial
interface immediately or to start the transmission process only after released by
the application. The latter is useful when data has to be transmitted on the serial
Manual
Version 1.4.0
Function Description 33