Technical data

WAGO-I/O-SYSTEM 750 Function Description 37
750-652 Serial Interface RS-232 / RS-485
Manual
Version 1.3.0
5.1.3.3 Flow Control Using RTS/CTS, RTS with Lead/Follow-on Time
With firmware version 03 or higher, the I/O module allows RTS/CTS for
communication with serial devices that only support a half-duplex connection.
This is important, for example, for communication with some telecontrol
modems.
If this type of flow control is activated, the I/O module sets RTS while it transmits
data to the serial interface. This allows the serial device to switch between receive
and transmit depending on RTS. Depending on the technology of the serial
device, the switch can take some time. Therefore, the I/O module can be
configured to set RTS already some time before transmission of the first character
(RTS lead time) or RTS resets only some time after transmission of the last
character (RTS follow-on time).
The RTS lead time and RTS follow-on time can be configured independent of
each other within the valid rage of 0 to 1000 ms.
If RTS is activated with lead time, the current state of the CTS input is
represented by the CTS bit changing in status byte 1.
5.1.4 RS-485 Operating Mode
The RS-485 operating mode in half-duplex is realized in a 2-wire multi-endpoint
(bus) connection. Simultaneous transmission and receiving is not possible with
2-wire connections. The I/O module switches to receive mode after transmitting
the content of the input buffer to the serial interface completely.
The the "RS-485 switching time" parameter can be used to configure the time
frame when the I/O module should switch after transmitting the last character can
be configured.
Possible settings are:
• 100 µs (default setting)
• Duration of the transfer of two characters with the current configuration
• Duration of the transfer of four characters at the current configuration
5.1.5 RS-422 Operating Mode
The RS-422 operating mode in full-duplex is realized in a 4-wire point-to-point
connection. Simultaneous transmission and receiving is thus possible.
In this mode, the I/O module supports flow control for the serial interface using
the XON/XOFF protocol (see chapter "Flow Control Using XON-/XOFF
Protocol").