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HP289
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 configured with a unique address which is used
by the Master Controller (e.g., an 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