DVDO VP50 PRO - Manual (Page 14)

1 RS-232 Control
1.1 The RS-232 Physical Connection
RS-232 connections come in several styles which are accepted in the consumer
electronics industry. The most common is the 9-pin D-Subminiature connector found on
the back of most computers, and is the one that we use on the iScan VP
xx
products.
The female serial port, found on the back panel of an iScan VP
xx
video processor.
In this interface, there are a few different signals which must be supported. These are
(all pin numbers are for the iScan):
RX – Data Receive (pin 3)
TX – Data Transmit (pin 2)
RTS – Request To Send (pin 8)
CTS – Clear To Send (pin 7)
GND – Signal Ground (pin 5)
We do not use the “DSR – Data Set Ready”, “DTR – Data Terminal Ready”, “CD -
Carrier Detect” or “RI – Ring Indicator” pins for the iScan VP
xx
series.
These signals are associated with specific pin numbers based on what type of device
the serial port is attached to. There are two types of serial device Data-Terminal-
Equipment (DTE) and Data-Communications-Equipment (DCE). A DTE is your
computer or an automation system – basically a controlling device. A DCE is a modem,
or in this case the iScan. Some manufacturers chose to wire their RS-232 port as a DTE,
but we have elected to wire our unit as a DCE. This determines a critical difference in
the serial cable wiring to get the unit to communicate with the automation controller or
PC. If your automation controller is based on a PC, the serial port is likely to be wired as
a DTE port (please check with your automation controller vendor for clarification). This
allows the use of a very common straight-through “extension” cable to be used to
complete the communication connection (like the type which is shipped with the iScan
unit).
When a dissimilar port type is used in a serial connection (for example DTE-to-DCE
or vise versa), a straight-through cable is usually all that is needed. However, when
similar port types are used, a cross-over cable is required (for example DCE-to-DCE or
DTE-to DTE). Please double check the type of connection that you are using before
connecting the cable.
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