40 Function Description
WAGO-I/O-SYSTEM 750 XTR
750-652/040-000 Serial Interface RS-232/RS-485 XTR
Manual
Version 1.3.0
5.1.3
RS-232 Operating Mode
The RS-232 operating mode in full-duplex is realized in a 2-wire or 4-wire point-to-
point connection. Simultaneous transmission and receiving is possible.
In this mode, the I/O module supports flow control for the serial interface. The I/O
module can be set, so that flow control occurs using of one of the following
methods:
•
XON-/XOFF protocol
•
RTS/CTS
•
RTS/CTS, RTS with lead / follow-on time
5.1.3.1 Flow Control Using XON-/XOFF Protocol
If flow control is activated using XON-/XOFF protocol, the I/O modules stops
transmitting data to the serial interface when it receives the XOFF character
(DC3==0x13) from the serial device. The I/O module continues transmitting data
when it receives the XON character (DC1==0x11). When data is received, the I/O
module monitors input buffer usage. It transmits the XOFF control character to the
serial device when the number of characters in the input buffer exceeds 2304. If
the number of characters in the input buffer is below 2176, it transmits XON.
5.1.3.2 Flow Control Using RTS/CTS
If flow control is activated using RTS/CTS, the I/O module stops transmitting data
to the serial interface when CTS is set. The I/O module continues transmitting data
when CTS is reset. When data is received, the I/O module monitors input buffer
usage. It sets RTS when the number of characters in the input buffer exceeds
2304. If the number of characters in the input buffer is below 2176, the I/O module
resets RTS.
5.1.3.3 Flow Control Using RTS/CTS, RTS with Lead/Follow-on Time
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.
