CC2400 Datasheet, PDF (31/84 Pages) Texas Instruments – 2.4 GHz Low-Power RF Transceiver

CC2400
23.3 Hardware interface
In the buffered mode the PKT pin can be
used as an interrupt output to assist the
microcontroller in supervising the
transmission and reception of data
packets.
The PKT pin can be programmed to give
an interrupt when the synthesizer has
locked and is ready to receive / transmit a
data packet. Receive mode or transmit
mode can then be activated.
In receive mode there will be an interrupt
when the synchronization word is found.
Incoming data will then be written to the
FIFO.
In transmit mode there will be an interrupt
when the FIFO has run empty, the two
CRC bytes have been transmitted and the
transmitter has been turned off.
Outside of the TX and RX modes, the PKT
pin provides an indication of whether the
PLL is in lock or not. For example, in the
FSON state, the PKT pin will be high if the
PLL is in lock.
The PKT pin activity is illustrated in Figure
10.
The polarity of the interrupt signal is set by
the INT.PKT_POLARITY bit.
In transmit mode, the PKT pin will go low
for a short while when the transmission is
completely over (the CRC has been sent).
In receive mode, the PKT pin will go low
when a sync word is found. It will stay low
for the period of time it would take to
receive 32 bytes, no matter how long the
received packet is (the CC2400 does not
know how long incoming packets are).
24 Data / Line Encoding
The CC2400 can operate with the following
line-encoding formats:
• NRZ (Non-Return-to-Zero)
• Manchester coding (also known
as bi-phase-level)
• 8/10 coding
The data format is controlled by the
GRMDM.DATA_FORMAT[1:0]
bits.
Manchester coding and 8/10 coding
reduce the effective bit rate but are in
some applications used for spectral
properties and error detection.
Manchester coding means coding each bit
into two chips of opposite polarity. The
Manchester code is based on transitions;
a “0” is encoded as a low-to-high
transition, a “1” is encoded as a high-to-
low transition. See Figure 14. The
Manchester code ensures that the signal
has a constant DC component, which is
necessary in some FSK demodulators.
This is not required by the CC2400
demodulator, but the coding option is
included for compatibility reasons. The
effective bit rate is half the baud rate using
Manchester coding.
8/10 coding means that 8 bits are coded
into 10 chips using the original IBM
8B/10B-coding scheme. The effective bit
rate is 80 % of the baud rate using 8/10
coding and is therefore more efficient that
the Manchester coding.
The benefit of the Manchester coding and
8/10 coding is the whitening of the
transmission spectrum even when rows of
equal bits are to be transmitted, improved
clock recovery properties and DC balance.
Setting the MDMTST0.INVERT_DATA bit
the data is inverted before transmission in
TX mode and inverted after reception in
RX mode.
24.1 Data encoding in buffered mode
In the buffered mode, using the internal
FIFO, all three line-encoding schemes can
be used.
The encoding/decoding takes place as the
data is sent from the FIFO to the
modulator, and from the demodulator to
the FIFO. The line encoding is therefore
invisible to the user.
SWRS042A
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