B&B Electronics MESR9xx Manual De Usuario

RS-232 connections support eight signal lines plus Signal Ground. Signals are single 
ended and referenced to Ground. Default communications parameters are 9600, 8, N, 1 
and no flow control implemented.  

RS-422 connections support two signal pairs: RXA(-), RXB(+) and TXA(-), TXA(+), 
plus GND. The data lines are differential pairs (A & B) in which the B line is positive 
relative to the A line in the idle (mark) state. Ground provides a common mode reference.  

RS-485 connections support 2-wire or 4-wire operation.  

When configured for 4-wire operation the connection supports two signal pairs: RXA(-), 
RXB(+) and TXA(-), TXA(+), plus GND. This makes full-duplex operation possible. 
The data lines are differential pairs (A & B) in which the B line is positive relative to the 
A line in the idle (mark) state. Ground provides a common mode reference.  

When configured for 2-wire operation the connection supports one signal pair: DataB(+) 
and DataA(-) signal channels using half-duplex operation. The data lines are differential 
with the Data B line positive relative to Data A in the idle (mark) state. Ground provides 
a common mode reference. 

The  MESR9x1-x has one serial connection that supports RS-232, RS-422 and RS-485 
(2- and 4-wire). The unit has two connectors: a DB-9M connector and a 5-position 
terminal block.  

If you select RS-232 mode when you configure the Modbus gateway, you must connect 
the Modbus network to the Modbus gateway via a serial cable. The MESR901 is a DTE. 
If the Modbus network is a DTE, use a null modem (cross-over) cable. If the Modbus 
network is a DCE, use a straight-through cable.  

If you select RS-422 mode, RS-485 2-wire mode, or RS-485 4-wire mode when you 
configure the Modbus gateway, you must connect the Modbus network appropriately, via 
the 5-position terminal block.