Vision Systems VScom 200E PCIex Manual de usuario descargar pdf (Pagina 49)

7 Proper Cabling in RS 485 and RS 422

7.5 4-Wire Scheme

RS 422 requires dedicated wire pairs for transmit and receive. The transmit wires are used to

send data to as many as 10 receivers, as stated in the speciﬁcations of RS 422. Since the VScom

Industrial Card uses RS 485 line driver technology, up to 32 receivers are possible.

While one pair is used to transmit, a second pair is available to receive data at the same time. When

only two devices are connected, this is a possible replacement of classic RS 232 connections.

In RS 485 4-wire mode the transmit wires may be shared between dedicated stations. As an example

a second station can be a backup master for the network. Masters can send data and commands

to one station, while they receive information from another device.

Figure 27: 4-Wire Cabling Scheme

Figure 27 displays the wire pairs Tx± and Rx± as named for Devices 1 and 2. There are more

slave devices, two are shown. The slaves transmit on the Rx-lines, and receive on the Tx-lines. The

GND line is also connected, to implement the Common Voltage Range as speciﬁed

Masters on the network are identiﬁed because they transmit on the Tx-lines. The two Masters in

ﬁgure 27 have to synchronize their use of the Tx-lines be extra means. E.g. Dev 2 can be a backup

master, which is manually activated.

Also indicated in ﬁgure 27 are polarization resistors P1/P2 for Tx± and P3/P4 for Rx±, only once

per wire pair. Further Termination resistors T1/T2 for Tx± and T3/T4 for Rx± are added, one at

each end of the cable. To ensure the Common Voltage Range the GND is also connected at each

device.

See 7.3 for isolated VScom Industrial Card

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Vision Systems VScom 200E PCIex Manual de usuario Pagina 49