Appendix C
Serial Port Information
©
National Instruments Corporation
C-5
PCI Serial for Windows 95
connector that contains embedded terminating resistors for easy
termination.
Figure C-3 shows a multidrop network using terminating resistors.
Figure C-3. Multidrop Network Using Terminating Resistors
Bias Resistors
A transmission line enters an indeterminate state if no nodes are
transmitting on it. This indeterminate state can cause the receivers to
receive invalid data bits from noise picked up on the cable. To prevent these
data bits, you should force the transmission line into a known state. By
installing two 620
Ω
bias resistors at one node on the transmission line, you
can create a voltage divider that forces the voltage between the differential
pair to be less than 200 mV, the threshold voltage for the receiver. You
should install these resistors on only one node.
MASTER
Slave 1
100
Ω
Slave 2
Slave n
100
Ω
Tx
Tx
Rx
Tx
Rx
Tx
Rx
Rx