B.4.4.2 RS-485
The RCM3400 Prototyping Board has one RS-485 serial channel, which is connected to
the Rabbit 3000 Serial Port E through an RS-485 transceiver. The half-duplex communi-
cation uses an output from PD0 on the Rabbit 3000 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.
Serial Port E is configured in software for RS-485 as follows.
#define
#define
#define
#define
#define
#define
ser485open serEopen
ser485close serEclose
ser485wrFlush serEwrFlush
ser485rdFlush serErdFlush
ser485putc serEputc
ser485getc serEgetc
#define EINBUFSIZE 15
#define EOUTBUFSIZE 15
#ifndef _485BAUD
#define _485BAUD 115200
#endif
The configuration shown above is based on circular buffers. RS-485 configuration may
also be done using functions from the PACKET.LIB library.
The RCM3400 Prototyping Boards with RCM3400 modules installed 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 B-8. Note that a common ground is recommended.
Figure B-8. RCM3400 Multidrop Network
86
RabbitCore RCM3400
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