Z-World eDisplay OP7200, User Manual

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28 eDisplay (OP7200)
3.5 Serial Communication
The OP7200 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 5 summarizes the options.
The OP7200 also has one RS-485 serial channel and a CMOS serial channel that serves as
the programming port.
All four serial ports operate in an asynchronous mode up to the baud rate of the system
clock divided by 32. 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 sup-
ported. Serial Port A, the programming port, and Serial Port B 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. When the Rabbit pro-
vides the clock, the baud rate can be up to ¼ of the system clock frequency, or more than
5.525 Mbps for a 22.1 MHz clock speed.
The OP7200 boards use all four serial ports. Serial Port A is used in the clocked serial
mode to provide cold-boot, download, and emulation functions. Serial Port B is used for
RS-485 communication, and Serial Ports C and D are used for RS-232 communication.
The OP7200 uses an 11.0592 MHz crystal, which is doubled to 22.1184 MHz. At this fre-
quency, the OP7200 supports standard asynchronous baud rates up to a maximum of
230,400 bps.
3.5.1 RS-232
The OP7200 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 OP7200’s maximum baud rate for distances of up to
15 m.
Table 5. Serial Communication Configurations
Software
Mode
Serial Port
B C D
0 RS-485 RS-232, 3-wire RS-232, 3-wire
1 RS-485 RS-232, 5-wire CTS/RTS