Table of Contents
Advertisement
The EIA RS-422 Specification labels data lines with "A" and "B"
designators. Some RS-422 equipment uses a "+" and "-"
designator. In almost all cases, the "A" line is the equivalent of the
"-" line and the "B" line is the equivalent of the "+" line.
Figure 6. P.C. Board for Optional RS-422/485 Port
RS-485 Mode
There are two methods that can be used to control the RS-
422/485 driver: handshake control (RTS) and send data (SD)
control. These methods are jumper selectable (JP1 "SD" & "RTS").
Handshake control requires that the software use a handshake
signal to enable/disable the RS-485 driver. The handshake signal
RTS (pin 4) is used when the master port is configured as a DCE
port and CTS (pin 5) is used when the master port is configured as
a DTE port.
SD control automatically enables the RS-485 driver by sensing
the leading edge of the first character transmitted from the device
connected to the master port. After the last character is transmitted
the send data timer circuit waits one character time (1 millisecond
at 9600 baud) before disabling the RS-485 driver.
There are two components on the main printed circuit board, a
resistor (R1) and a capacitor (C1), that are part of the send data
control circuit. These components are factory selected for 9600
baud, which allows the send data control to operate at 9600 baud or
higher. With these two components the RS-485 driver will be
disabled approximately 1 millisecond after the last character has
8
B&B Electronics -- PO Box 1040 -- Ottawa, IL 61350
PH (815) 433-5100 -- FAX (815) 434-7094
232PE3095 Manual
Advertisement
Table of Contents
