Table A-2: Rs422 Specification Summary - IBM LPCI-COM-8SM User Manual

Low profile pci multi-port serial communications cards

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A maximum common mode voltage rating of +7V provides good noise immunity from voltages

induced on the twisted pair lines. The signal ground line connection is necessary in order to

keep the common mode voltage within that range. The circuit may operate without the ground

connection but may not be reliable.

Parameter

Driver Output Voltage (unloaded)

Driver Output Voltage (loaded)

Driver Output Resistance

Driver Output Short-Circuit Current

Driver Output Rise Time

Receiver Sensitivity

Receiver Common Mode Voltage Range

Receiver Input Resistance

To prevent signal reflections in the cable and to improve noise rejection in both the RS422 and

RS485 mode, the receiver end of the cable should be terminated with a resistance equal to the

characteristic impedance of the cable. (An exception to this is the case where the line is driven

by an RS422 driver that is never "tristated" or disconnected from the line. In this case, the driver

provides a low internal impedance that terminates the line at that end.)

Note

You do not have to add a terminator resistor to your cables when you use the card. Termination

resistors for the RX+ and RX- lines are provided on the card and are placed in the circuit when

you install the Ch X - LD jumpers. (See the Option Selection section of this manual.)