Yokogawa 414 Batch Controller Manual do Utilizador descarregar pdf (Página 28)

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4.1.2 Multipoint Communication

Multipoint Communication is a system whereby a number of instruments can be

addressed over a dual twisted pair interface. Up to 32 instruments can be

connected to a common bus using the RS422 and RS485 interfaces as shown

below.

To convert the RS422 interface to an RS485 interface, the RS422 (-) Data In

Terminal must be connected to the RS422 (-) Data Out Terminal and the RS422

(+) Data In Terminal must be connected to the RS422 (+) Data Out Terminal.

These connections will convert the RS422 4 wire interface to the RS485 2 wire

interface, as shown in figure 2.

Each instrument can be programmed with a unique address which is used by the

Master Controller (ie. IBM/PC) to identify each instrument. The Controller will

send the address down the line and will alert the relevant instrument. Subsequent

software protocol will control the flow of data between the Controller and the

Instrument.

Figure 1 RS422 Interface

Host

Computer

400 Series

Instrument

400 Series

Instrument

Load

120 ohms

Load

120 ohms

Twisted Pair

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Yokogawa 414 Batch Controller Manual do Utilizador Página 28