Rabbit Smartcat, Руководство пользователя

Страница: 29 / 135

User’s Manual 23
3.3 Serial Communication
The BL2100 has two RS-232 serial ports, which can be configured as one RS-232 serial
channel (with RTS/CTS) or as two RS-232 (3-wire) channels using the
serMode
software
function call. Table 2 summarizes the options.
The BL2100 also has one RS-485 serial channel and one CMOS serial channel that serves
as the programming port.
All four serial ports operate in an asynchronous mode. An asynchronous port can handle 7
or 8 data bits. A 9th bit address scheme, where an additional bit is sent to mark the first
byte of a message, is also supported. Serial Port A, the programming port, can be operated
alternately in the clocked serial mode. In this mode, a clock line synchronously clocks the
data in or out. Either of the two communicating devices can supply the clock. The BL2100
boards typically use all four ports in the asynchronous serial mode. Serial Ports B and C
are used for RS-232 communication, and Serial Port D is used for RS-485 communica-
tion. The BL2100 uses an 11.0592 MHz crystal, which is doubled to 22.1184 MHz. At this
frequency, the BL2100 supports standard asynchronous baud rates up to a maximum of
230,400 bps.
3.3.1 RS-232
The BL2100 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
2000’s CMOS/TTL signals to RS-232 signal levels. Note that the polarity is reversed in an
RS-232 circuit so that a +5 V output becomes approximately -10 V and 0 V is output as
+10 V. The RS-232 transceiver also provides the proper line loading for reliable commu-
nication.
RS-232 can be used effectively at the BL2100’s maximum baud rate for distances of up to
15 m.
3.3.2 RS-485
The BL2100 has one RS-485 serial channel, which is connected to the Rabbit 2000 Serial
Port D through an RS-485 transceiver. The half-duplex communication uses the Rabbit
2000’s PB6 pin to control the transmit enable on the communication line.
Table 2. Serial Communication Configurations
Mode
Serial Port
B C D
0 RS-232, 3-wire RS-232, 3-wire RS-485
1 RS-232, 5-wire CTS/RTS RS-485