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4-10
Chapter 4: Appendices – RS-485/422 Interface
Full Duplex Mode
By not installing pins on jumper block JA and by using features
in our driver software, you can run the individual RS-485/422
ports in full duplex mode. This mode is typically used in point to
point RS-485/422 situations much like RS-232. In this mode,
TxD & RxD are active all the time. Figure 1 shows the location
of jumper block JA.
Half Duplex RS-485
By installing pins on jumper block JA and using features in our
driver software, you can run the individual RS-485/422 ports in
half duplex mode. In this mode your Titan/cPCI adapter controls
the transmitter and receiver circuits. DTR is turned on prior to
and during transmission to cause the transmit driver to enable and
the receiver to disable. DTR is turned off when not transmitting
to cause the transmit driver to disable (tri-stated) and the receiver
to enable. The 16C950 UARTs on the Titan/cPCI adapter are
responsible for timing the DTR toggle.
Multi-drop Slave Mode
By not installing jumpers on jumper block JA and by using
features in our driver software, you can run the individual RS-
485/422 ports in multi-drop slave mode. In this mode the TxD
line driver is enabled only when data is transmitted and RxD is
enabled all the time. This mode is typically used in multi-drop "4
wire" connections.
Example
The example below shows the settings on JA where RS-485
ports 1 and 2 are set for full duplex or multi-drop slave mode,
port 3 is set for half duplex and port 4 is not set since port 4 is
set for RS-232 on jumper block JB.
Technical Note:
Full duplex, multi-drop slave and half duplex modes apply to
RS-485/422 ports only. Please ensure that the port is set for
RS-485/422 on jumper block JB.
Titan/cPCI User's Manual, ver. 0.00
JA
Jumper Legend
Port 1
JA0
Jumpers on = ½ duplex enabled
Port 2
JA1
JA2
Port 3
4 port models
Port 4
JA3
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