Texas Instruments CC900DB, Руководство пользователя, Страница: 9 / 20

SWRU064
9
3 Demonstration Board software description
The demonstration board software is implemented in assembly and runs on the Atmel
AVR 8-bit micro-controller ATtiny12L.
The micro-controller handles the CC900 configuration, data encoding and decoding
using Manchester code, and implements a simple packet protocol.
A program listing with the assembly source code is available for reference and can be
used as a starting point for your own applications using the AVR series of controllers
from Atmel.
3.1 Sleep mode
When the CC900DB is left inactive for approximately one minute the CC900 is set to
power down mode, and the controller goes to “sleep”. The controller is awaked by an
interrupt signal at INT1 (pin 6).
In sleep mode the current consumption is less than 1
µ
A.
3.2 Active mode
In active mode the CC900 is used for receive polling. Once every second the CC900 is
set to RX mode, and the micro-controller starts searching for a preamble. The micro-
controller reads two data bits, if these are not Manchester coded 1’s, the CC900 is set to
power down mode again. The LED is lit during the pre-amble search and will appear as
a “heartbeat” signal.
In active mode the “TX” button input (PB2) is also monitored. If this line is pulled low
by the push button, the micro-controller will configure the CC900 to TX mode, and send
a predefined data packet at the DIO line (PB1), before returning to receiver polling.
3.3 Data packet description
The data packet consists of a pre-amble, a start-of-frame (SOF), and a data field.
The pre-amble is a train of ‘1’s. The train is longer than 1 second in order to ensure that
it intercept with a polled receiver.
The SOF consists of two consecutive ‘0’s. The SOF marks the end of the preamble, and
the start of the actual data.
The data field consists of ID (identification), TYPE (packet type) and DATA (user data,
3 bytes). No FEC (forward error correction) or CRC (cyclic redundancy check) is used
in order to keep it as simple as possible.