CC2420
Data in RXFIFO
Length byte
n | MPDU1 | MPDU2 |
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MPDU
RSSI |
|
CRC / Corr |
Bit number | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
| CRC | Correlation value (unsigned) | ||||||
| OK | |||||||
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|
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| |
Figure 21. Data in RXFIFO when MDMCTRL0.AUTOCRC is set
17RF Data Buffering
CC2420 can be configured for different transmit and receive modes, as set in the
MDMCTRL1.TX_MODEand MDMCTRL1.RX_MODE control bits. Buffered mode (mode 0) will be used for normal operation of CC2420, while other modes are available for test purposes.
17.1 Buffered transmit mode
In buffered transmit mode (TX_MODE 0), the 128 byte TXFIFO, located in CC2420 RAM, is used to buffer data before transmission. A preamble sequence (defined in the Frame Format section below) is automatically inserted before the length field during transmission. The length field must always be the first byte written to the transmit buffer for all frames.
Writing one or multiple bytes to the TXFIFO is described in the FIFO access section on page 31. Reading data from the TXFIFO is possible with RAM access, but this does not remove the byte from the FIFO.
Transmission is enabled by issuing a STXON or STXONCCA command strobe. See the Radio control state machine section on page 43 for an illustration of how the transmit command strobes affect the state of CC2420. The STXONCCA strobe is ignored if the channel is busy. See the Clear Channel Assessment section on page 50 for details on CCA.
The preamble sequence is started 12 symbol periods after the command strobe. After the programmable start of frame delimiter has been transmitted, data is fetched from the TXFIFO.
A TXFIFO underflow is issued if too few bytes are written to the TXFIFO. Transmission is then automatically stopped. The underflow is indicated in the TX_UNDERFLOW status bit, which is returned during each address byte and each byte written to the TXFIFO. The underflow bit is only cleared by issuing a SFLUSHTX command strobe.
The TXFIFO can only contain one data frame at a given time.
After complete transmission of a data frame, the TXFIFO is automatically refilled with the last transmitted frame. Issuing a new STXON or STXONCCA command strobe will then cause CC2420 to retransmit the last frame.
Writing to the TXFIFO after a frame has been transmitted will cause the TXFIFO to be automatically flushed before the new byte is written. The only exception is if a TXFIFO underflow has occurred, then a SFLUSHTX command strobe is required.
17.2 Buffered receive mode
In buffered receive mode (RX_MODE 0), the 128 byte RXFIFO, located in CC2420 RAM, is used to buffer data received by the demodulator. Accessing data in the RXFIFO is described in the FIFO access section on page 31.
The FIFO and FIFOP pins are used to assist the microcontroller in supervising the RXFIFO. Please note that the FIFO and FIFOP pins are only related to the RXFIFO, even if CC2420 is in transmit mode.
SWRS041B | Page 39 of 89 |
