ICOM-2S Manual
A-2
Manual MICOM-2S.Eb
A balanced differential line receiver senses the voltage state of the transmission line across the two
signal input lines. If the differential input voltage is greater than +200 mV, the receiver will provide
a specific logic state on its output. If the differential voltage input is less than -200 mV, the receiver
will provide the opposite logic state on its output. A maximum operating voltage range is from +6V
to -6V allows for voltage attenuation that can occur on long transmission cables.
The maximum common mode voltage rating 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
Conditions
Min.
Max.
Driver Output Voltage (unloaded)
4V
6V
-4V
-6V
Driver Output Voltage (loaded)
LD and LDGND
2V
jumpers in
-2V
Driver Output Resistance
50
?
Driver Output Short-Circuit Current
±150 mA
Driver Output Rise Time
10% unit interval
Receiver Sensitivity
±200 mV
Receiver Common Mode Voltage Range
±7V
Receiver Input Resistance
4K
?
Table A-2:
RS422 Specification Summary
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 ICOM-2S card.
Termination resistors for the RX+ and RX- lines are provided on the card and are placed in the circuit
when you install the LD and LDGND jumpers. Moreover, installing the +BIAS and -BIAS jumpers
properly biases these lines. (See the Option Selection section of this manual.)
Summary of Contents for ICOM-2S
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