Adastra Systems NPC-486E, Руководство пользователя

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Multi-drop support allows several RS-485 transmitters to share a single (half duplex)
channel. Software protocol insures that only one transmitter is active at any one time.
RS-485
Data
Out
Transmitter 1
Enable
Multi-Drop
Data
In
Data
Out
Transmitter 2
Enable
Data
In
Data
Out
Transmitter 3
Enable
Data
In
(+)
(-)
In a multi-drop environment the transmitter is enabled only when necessary. A software
protocol typically controls which RS-485 node has permission to transmit. The authorized
transmitter asserts it’s transmit enable and transmits all necessary data. When finished, the
transmitter should be disabled.
In the RS-485 implementation of multi-drop of the NPC-486E, the transmitter enable line
is controlled by bit 5 of Custom I/O register 0. The transmitter is enabled by writing a “1”
to the bit and is disabled by writing a “0”.
7 6 5 4 3 2 1 0
C u s t o m R e g ister #0
B it
H a lf D u p l e x T r a n s m i t C o n t r o l
0 : T r a n s m i t D i s a b l e d
1 : T r a n s m i t E n a b l e d
0: RS-485 Enabled