Z-World eDisplay OP7200, Руководство пользователя

Страница: 35 / 152

User’s Manual 29
3.5.2 RS-485
The OP7200 has one RS-485 serial channel, which is connected to the Rabbit 2000 Serial
Port B through an RS-485 transceiver. The half-duplex communication uses an output
from the CPLD (U4) to control the transmit enable on the communication line. Using this
scheme a strict master/slave relationship must exist between devices to insure that no two
devices attempt to drive the bus simultaneously.
The OP7200 can be used in an RS-485 multidrop network spanning up to 1200 m (4000 ft),
and there can be as many as 32 attached devices. Connect the 485+ to 485+ and 485– to
485– using single twisted-pair wires as shown in Figure 14. Note that a common ground is
recommended.
Figure 14. OP7200 Multidrop Network
RS-485–
RS485+
GND
RS-485–
RS485+
GND
RS-485–
RS485+
GND