Connect Tech Blue Heat/PCI PCI Serial Communications Appendix C: RS-422/485 Line Interface

Blue Heat/PCI User’s Manual, Connect Tech Inc.

31 Revision 0.11

Appendix C: RS-422/485 Line Interface

For information on how to configure your RS-422/485 interface, find your specific Blue

Heat/PCI model below:

You can order the Blue Heat/PCI RS-422/485 adapter with all ports RS-422/485 or a

combination of RS-422/485 and RS-232. The RS-422/485 electrical interface is a reliable high-

speed serial link that offers superior noise immunity and multi-drop network connectivity. The

RS-422/485 electrical interface is also a superset of the RS-422 electrical interface. The Blue

Heat/PCI RS-422/485 offers full RS-422/485 support in hardware. The modes are as follows:

Full Duplex Mode

In this mode, TxD & RxD are active all the time. This mode is typically used in point to point

situations much like RS-232.

Half Duplex Mode

In this mode the TxD line driver is enabled only when data is transmitted and RxD is disabled

when data is being transmitted. This mode is typically used in either point to point "2 wire"

connections OR in multi-drop "2 wire" bus connections.

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.

Line Bias/Termination

On the Blue Heat/PCI RS-422/485 the RS-422/485 receivers are biased high through fixed

resistors. Please refer to Figure 11 for a partial schematic.

Universal Blue Heat/PCI RS-422/485 adapters offer full RS-422/485 support in hardware like

the other Blue Heat/PCI RS-422/485 models. The modes include full duplex, half duplex, and

multi-drop slave. Universal Blue Heat/PCI RS-422/485 adapters offer the following additional

functionality:

Tri-state Control

Universal Blue Heat/PCI RS-422/485 adapters allow you to tri-state the line drivers on power

up. To tri-state the drivers on power up please ensure there is no jumper installed across the pins

on jumper block JI. Refer to Figure 3 for the location of J1.

Line Bias/Termination

On the Universal Blue Heat/PCI RS-422/485 the RS-422/485 receivers are biased high through

fixed resistors. Please refer to Figure 11 for a partial schematic.