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.
JA
JA0 | Port 1 |
JA1 | Port 2 |
JA2 | Port 3 |
JA3 | Port 4 |
Jumper Legend
Jumpers on = ½ duplex enabled
4 port models
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
