58
W&T
USB Interfaces
Integrated overvoltage protection
The permissible voltages which are allowed to affect serial
interfaces in fault situations are limited to rather low values
according to the data sheets of the interface chips used here.
Voltages which exceed these values will inevitably result in
destruction of or damage to the interface components.
To prevent such effects, the USB Interface Model 38211 has
integrated overvoltage protection, which uses protection
diodes to limit the maximum voltages which can occur to
non-harmful values in a variety of applications.
This overvoltage protection of course is limited by the capacity
of the diodes used, which can carry a current of 20A for a brief
time, and cannot replace any major protection which might be
required for long cables used outdoors (e.g. in the mountains).
Wiring configuration
The serial connection on the Interface is configured as a
DB9 plug. The pin configuration can be found in the following
tables:
RS232 mode
RS422/RS485 mode
pin#
signal
function
1
DCD
input
2
RxD
input
3
TxD
output
4
DTR
output
5
GND
GND
6
DSR
input
7
RTS
output
8
CTS
input
9
RI
input
pin#
signal
function
1
TXD A
output
2
RxD A
input
3
DTR A
output
4
CTS A
input
5
GND
GND
6
TXD B
output
7
RxD B
input
8
DTR B
output
9
CTS B
input
