User`s manual

12 RabbitCore 2000
2.4 Serial Communication
The RabbitCore 2000 does not have an RS-232 or an RS-485 transceiver directly on the
RabbitCore 2000 board. However, the Prototyping Board does support a industry stan-
dard RS-232 transceiver chip. See Appendix B, “Prototyping Board,” for more informa-
tion.
2.4.1 Serial Ports
There are four serial ports designated as Serial Ports A, B, C, and D. All four serial ports
can 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 supported. Serial ports A
and 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 provides the clock, the baud rate can be up to 1/4 of the
system clock frequency, or more than 6.45 Mbps for a 25.8 MHz clock speed.
2.4.2 Programming Port
Serial Port A has special features that allow it to cold-boot the system after reset. Serial
Port A is also the port that is used for software development under Dynamic C.
The RabbitCore 2000 has a 10-pin program header labeled J3. The Rabbit 2000 startup-
mode pins (SMODE0, SMODE1) are presented to the programming port so that an exter-
nally connected device can force the RabbitCore 2000 to start up in an external bootstrap
mode. The Rabbit 2000 Microprocessor User’s Manual provides more information
related to the bootstrap mode.
The programming port is used to start the RabbitCore 2000 in a mode where it will down-
load a program from the port and then execute the program. The programming port trans-
mits information to and from a PC while a program is being debugged.
The RabbitCore 2000 can be reset from the programming port via the /RESET_IN line.
The Rabbit 2000 status pin is also presented to the programming port. The status pin is an
output that can be used to send a general digital signal.
The clock line for Serial Port A is presented to the programming port, which makes fast
serial communication possible.