Serial Interface (SI) setting


(see setting description format info here)

Function:Selects full-duplex or half-duplex mode for the serial port of the DS (when in the data routing mode)
Set (S) command format:SSIx, where x: 0 (full-duplex), 1 (half-duplex), 2 (auto)
Get (G) command format:GSI
Init (I) command effect:Initialized unconditionally, through network command, serial command, or quick initialization
Post-initialization value:2 (auto)
Change takes effect:After reboot or exiting the serial programming mode
Overriding parameter:---
Relevance conditions:---
First introduced:Earlier than "baseline" V3.14/V3.51
See also:Serial port and serial communications


Serial port of the DS can operate in full-duplex or half-duplex mode. "Full-duplex" and "half-duplex" here refers exclusively to the logical operation of the DS, not to the hardware implementation of the serial port, which depends on the DS model.

The setting only influences the operation of the serial port in the data routing mode . When the serial port is in the serial programming mode it is always using the half-duplex interface- see serial programming for details.

0 (full-duplex)Suitable for RS232 and RS422 communications. RTS (output) and CTS (input) lines are used in a "normal" way i.e. for flow control between the DS and attached serial device (when current Flow Control (FC) [setting/ parameter]= 1 (enabled)), or signaling between the network host and attached serial device (through Set I/O Pin Status (Sx) instructions, Get I/O Pin Status (Gx) instructions, and Notification (J) messages).
1 (half-duplex)Suitable for RS485 communications. In this mode the RTS line provides direction control and the CTS line is unused. When the Ethernet-to-serial buffer of the DS is empty (nothing to send out through the serial port) the RTS line is HI*. When there is some data to send out the RTS line is LOW* for as long as the data is being output. Such behavior is intended to allow the RTS line to control the direction pin of the RS485 interface ICs and RS232-to-RS485 converters.
2 (auto)In this mode the DS selects full-duplex or half-duplex mode automatically, depending on the hardware. For Ethernet Modules selection is done by interconnecting or not interconnecting a pair of I/O pins. External Device Servers carry necessary selection circuit internally. Table below details interface selection through "hardware".

Hardware selection of full-duplex/half-duplex mode on Tibbo Device Servers

When Serial Interface is at 2 (auto) the DS selects full-duplex or half-duplex mode for its serial port basing on "hardware". Table below details hardware-based mode selection.

DS Model

For full-duplex mode

For half-duplex mode



Leave CTS/SEL and ER/WS unconnected

Connect CTS/SEL to ER/WS**




Leave CTS/SEL and SR unconnected

Connect CTS/SEL to SR**




Always selected


These products are based on the EM100; they only support RS232 i/f so CTS/SEL and ER/WS are left unconnected internally


Depends on jumpers


This product is based on the EM100; jumpers "decide" whether CTS/SEL and ER/WS are interconnected



Always selected


These products are based on the EM120 or EM200; they only support RS232 i/f so CTS/SEL and SR are left unconnected internally

* HI and LOW states are described with respect to the serial ports of DS100R, DS100B, DS203. For EM100, EM120, EM200, EM203(A) the signaling is exactly opposite.

** Whether or not these two lines are interconnected is tested once at powerup. Connecting or separating these line during device operation will not cause immediate change of selected interface mode.