CC2400-RTR1 datasheet(31/84 Pages) TI

31 / 84 page

CC2400

SWRS042A

Page 31 of 83

23.3 Hardware interface

In the buffered mode the PKT pin can be

used as an interrupt output to assist the

microcontroller

supervising

the

transmission

and

reception

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.

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