Horner-apg QX351 OCS HEQX351C103 Manuel d'utilisateur télécharger pdf (Page 27)

MAN0892-03-EN CH.5

February 25, 2010 Page 27 of 109 #1039

5.4 RS-485 Termination

Proper RS-485 termination minimizes reflections and improves reliability.

Both serial ports allow an internal RS-485 termination resistor to be placed across pins 1 and 2 by DIP

Switch Setting.

Only the two devices physically located at the endpoints of the RS-485 network should be terminated.

5.5 RS-485 Biasing

RS-485 biasing passively asserts a line-idle state when no device is actively transmitting, which is useful

for multi-drop RS-485 networking.

Both serial ports allow internal RS-485 bias resistors to be switched in, pulling pin 1 up to 3.3V and pulling

pin 2 down to ground. The Set Serial Ports item in the System Menu can be used to enable RS-485

biasing. Also, an application graphics screen that writes to %SR164 can do the same thing. Setting

%SR164.1 enables MJ1 biasing and setting %SR164.2 enables MJ2 biasing.

If biasing is used, it should be enabled in only one of the devices attached to the RS-485 network. It is

recommended to have single BIAS otherwise network may be more susceptible to electrical noise.

5.6 Cscape Programming via Serial Port

The QX351 OCS MJ1 and MJ2 serial ports support CsCAN Programming Protocol. If a PC COM port is

connected to the QX351 OCS MJ1/MJ2 serial port, Cscape can access the QX351 OCS for programming

and monitoring.

5.7 Ladder-Controlled Serial Communication

Using Serial Communication function blocks, both MJ1 and MJ2 support Generic, Modbus Master and

Modbus Slave Protocols. In addition, external modems can be connected and accessed using Init, Dial

and Answer Modem function blocks.

The DIP Switches are used for

termination of the RS-485

ports. The

QX351 is shipped un-terminated.

To terminate, select one of the DIP

Switches and configure it based upon

the option that is desired.

SW1 - ON enables MJ2 RS485 port

termination (121 Ohms).

OFF disables MJ2 RS485 port

termination.

SW2 & SW3 - ON places MJ2 RS485 port in

half-duplex mode.

OFF places MJ2 RS485 port in full-

duplex mode.

SW4 - ON enables MJ1 RS485 port

termination (121 Ohms).

OFF disables MJ1 RS485 port

termination.

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Horner-apg QX351 OCS HEQX351C103 Manuel d'utilisateur Page 27

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