User manual

Connect Tech Xtreme/104 Plus, PCI-104 and PCI/104 Express Family User Manual

Revision 0.11

18.5 Bias and Termination Resistors XIG 12 Port Opto

The (B&T) Bias and Termination resistors are use in RS485 communications. All other modes

these jumpers should be removed.

The B&T resistors are selected using jumpers Jx.1E/Jx.1F (4-wire networks) and Jx.2A/Jx.2B

(2-wire networks).

RXD and TXD/RXD Termination/Bias: Install this pair of jumpers to enable a 150 ohm

terminator across the RxD+/- signals for 4-wire modes, and TxD/RxD+/- for 2-wire modes for

the corresponding port. A biasing network is also enabled that drives the receiver to an inactive

or safe mode. The receiver can still receive data from another device and the biasing helps to

prevent the reception of data generated by noise on the transmission line. The two jumpers for

the termination/bias must be installed and removed as a pair.

Bias and Termination Notes:

 For 2-wire and 4-wire multidrop wiring networks the B&T resistors must only be

installed when the Xtreme/PCI-104 12 Port Opto is the first or last device in the wiring

network.

 4-wire networks must only use the Jx.1E/Jx.1F jumpers.

 2-wire networks must only use the Jx.2A/Jx.2B jumpers.

 Never have both pairs of B&T resistors installed!

18.6 Power-on Tri-state for XIG 12 Port Opto

The XIG offers a power-on tri-state feature to ensure glitch-free power-up on multi-drop

networks. When enabled, the Xtreme/104- Opto will hold the RS-485 transmitter in tri-state at

power up. This feature is available on ports configured as RS-485 half duplex or RS-485 4-wire

multi-drop.

Note: Enabling this feature on ports configured in RS-232 or RS-422 (RS-485 full duplex)

modes will disrupt the operation of the RTS signal.

Jumper G-485 in J2 controls the power-on tri-state functionality. Install a jumper on this jumper

to enable the Power on Tri-State function.

18.7 Power considerations for the XIG 12 Port Opto

Under worst case RS485 operations the XIG can draw significant current.

The XIG can draw up to 1400mA from the 5V rail under the most extreme RS485 conditions. Under these

condition the power dissipation is 1400mA*5V = 7 Watts. The conditions for this are as follows:

 All ports RS485 4-wire mode.

 Bias and Termination (B&T) circuit installed all ports (provides bias and termination on

the RX+/- signals).

 Remote end or device end with 120 ohm termination resistor installed.

 TX +/- and RTS +/- with external 120 ohm terminator installed all ports.

 31 remote devices connected per port.