USB232U/485Ui
Page iii
A.1.3 USB485Ui RS422/485 Port
A.1.3.1 9-way Connector
9-way, male D-type connector with metal shell. For the isolated
versions, all signals are referred to the remote device signal
ground.
A.1.3.2 Data Rate
The port is capable of error free transmission at data rates up
to 3 M Baud.
A.1.3.3 Rx I/P Termination
120
Ω
resistor across differential input terminals of Rx Data
receiver. For multi-drop applications, the Rx data line
termination resistor can be disconnected by removing a
jumper.
A.1.3.4 Tx O/P Protection
Excessive output current and power dissipation caused by
faults or bus contention are prevented by two mechanisms. A
fold-back current limit provides immediate protection against
short circuits and thermal protection forces the driver into a
high impedance state if the die temperature exceeds the limits.
A.1.3.5 I/O Isolation
For the isolated versions, each RS485 interface is electrically
isolated, with no common connections to the other port. Signal
isolation is by opto-couplers on the data lines and power to the
drivers/receivers is supplied through an isolated DC-DC
converter.
The design is such that it will sustain common mode voltages
up to 75Vdc, which is outside of the low voltage directive
(73/23/EEC). However in fault conditions they are protected to
sustain common mode voltages up to peaks of 1 kVdc.
A.1.3.6 ESD Protection
The RS422/485 line input/outputs have on-chip protection from
ESD transients up to ±8 kV for human body model discharges.
A.1.3.7 Modes
Full Duplex, Half Duplex, Multi-drop, Broadcast. The mode of
operation is jumper selectable see 2.3.1.1 and 2.3.1.2.
A.1.3.8 Transmit Turnaround
Transmission turn around is internal to the device. When in
half duplex mode, the transmitter is automatically enabled
when there is data to transmit.
Summary of Contents for USB232U
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