Rs-232 Operating Mode; Flow Control Using Xon-/Xoff Protocol; Flow Control Using Rts/Cts; Flow Control Using Rts/Cts, Rts With Lead/Follow-On Time - WAGO 750 Series Manual

34 Function Description
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 (firmware version 03 or higher)
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

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.
WAGO-I/O-SYSTEM 750
750-652 Serial Interface RS-232 / RS-485
Manual
1.2.0