Differential Input Termination
Each port on the card has optional termination of RS-422/485 differential inputs controlled by a six
position switch
labeled with a port number and the word ’TERM’
. Each position is labeled with a number
(1 at top through 6 at bottom). The
on position is to the right and is labeled ‘ON’.
When a switch is in the
ON position, the associated differential input is terminated with 120 ohms. By default all inputs are
terminated for all ports. Termination settings do not affect single ended (RS-232/V.28) inputs.
Termination increases signal reliability at high speeds (generally 1Mbps or more). At high speeds, inputs
at each end of a cable should be terminated. For a multi-drop setups (more than 2 devices on a cable),
do not terminate receivers connected to the middle of the cable. At slower speeds, the termination can
usually remain without problem. Removing termination at slower speeds may allow the use of longer
cables.
To disable termination on an input, move the associated switch position to OFF.
Switch Position Signal Name
1
TxC (Transmit Clock)
2
RxC (Receive Clock)
3
RxD (Receive Data)
4
CTS (Clear to Send)
5
DSR (Data Set Ready)
6
DCD (Data Carrier Detect)
