Rabbit Coyote BL2500, Руководство пользователя

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28 Coyote (BL2500)
3.5.1 RS-232
The Coyote RS-232 serial communication is supported by an RS-232 transceiver. This
transceiver provides the voltage output, slew rate, and input voltage immunity required to
meet the RS-232 serial communication protocol. Basically, the chip translates the Rabbit
3000’s CMOS/TTL signals to RS-232 signal levels. Note that the polarity is reversed in an
RS-232 circuit so that a +3.3 V output becomes approximately -6 V and 0 V is output as
+6 V. The RS-232 transceiver also provides the proper line loading for reliable communi-
cation.
RS-232 can be used effectively at the Coyote’s maximum baud rate for distances of up to
15 m.
RS-232 flow control on an RS-232 port is initiated in software using the
serXflowcontrolOn
function call from
RS232.LIB
, where
X
is the serial port (E or F).
The locations of the flow control lines are specified using a set of five macros.
SERX_RTS_PORT
—Data register for the parallel port that the RTS line is on (e.g., PGDR).
SERX_RTS_SHADOW
—Shadow register for the RTS line's parallel port (e.g., PGDRShadow).
SERX_RTS_BIT
—The bit number for the RTS line.
SERX_CTS_PORT —Data register for the parallel port that the CTS line is on (e.g., PCDRShadow).
SERX_CTS_BIT —The bit number for the CTS line.
Standard 3-wire RS-232 communication using Serial Ports E and F is illustrated in the fol-
lowing sample code.
#define EINBUFSIZE 15
#define EOUTBUFSIZE 15
#define FINBUFSIZE 15
#define FOUTBUFSIZE 15
#ifndef _232BAUD
#define _232BAUD 115200
#endif
main(){
serEopen(_232BAUD);
serFopen(_232BAUD);
serEwrFlush();
serErdFlush();
serFwrFlush();
serFrdFlush();
}