20-101-1051 Datasheet, PDF (100/165 Pages) List of Unclassifed Manufacturers – C-Programmable Core Module with NAND Flash Mass Storage and Ethernet

B.4.6.2 RS-485
The Prototyping Board has one RS-485 serial channel, which is connected to the Rabbit
3000 Serial Port C through an RS-485 transceiver. The half-duplex communication uses
an output from PD7 on the Rabbit 3000 to control the transmit enable on the communica-
tion 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 C is configured in software for RS-485 as follows.
#define ser485open serCopen
#define ser485close serCclose
#define ser485wrFlush serCwrFlush
#define ser485rdFlush serCrdFlush
#define ser485putc serCputc
#define ser485getc serCgetc
#define CINBUFSIZE 15
#define COUTBUFSIZE 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 Prototyping Boards with RCM3365/RCM3375 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. Multidrop Network
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RabbitCore RCM3365/RCM3375