CC2520_11 Datasheet, PDF (68/133 Pages) Texas Instruments – 2.4 GHZ IEEE 802.15.4/ZIGBEE RF TRANSCEIVER

CC2520 DATASHEET
2.4 GHZ IEEE 802.15.4/ZIGBEE® RF TRANSCEIVER
SWRS068 – DECEMBER 2007
Figure 16. Frame data written to the TX FIFO
There are three ways to write to the TX FIFO:
• The TXBUF instruction transfers bytes from the microcontroller to the TX FIFO in CC2520.
• The TXBUFCP instruction copies bytes from the general RAM in CC2520 into the TX FIFO.
• Frame buffering always begins at the start of the TX FIFO memory. By enabling the
FRMCTRL1.IGNORE_TX_UNDERF bit, it is possible to MEMWR, MEMCP and other memory
instructions to write the frame. Note, however, that using dedicated TXBUF and TXBUFCP
instructions should be preferred.
The number of bytes in the TX FIFO is stored in the TXFIFOCNT register.
The TX FIFO can be emptied manually with the SFLUSHTX command strobe. TX underflow will occur If the
FIFO is emptied during transmission.
19.3.1 Retransmission
In order to support simple retransmission of frames, the CC2520 does not delete TX FIFO contents as they
are transmitted. After a frame has been successfully transmitted, the FIFO contents are left unchanged. To
retransmit the same frame again, simply restart TX by issuing a STXON or STXONCCA command strobe.
If a different frame is to be transmitted, just write the new frame to the TX FIFO. In this case, the TX FIFO is
automatically flushed before the actual writing takes place.
19.3.2 Error Conditions
There are two error conditions associated with the TX FIFO:
• Overflow happens when the TX FIFO is full and it is attempted to write another byte.
• Underflow happens when the TX FIFO is empty and CC2520 attempts to fetch another byte for
transmission.
TX overflow is indicated by the TX_OVERFLOW exception. When this error occurs, the writing will be
aborted, i.e. the data byte that caused the overflow will be lost. The error condition must be cleared with the
SFLUSHTX strobe.
TX underflow is indicated by the TX_UNDERFLOW exception. When this error occurs, the ongoing
transmission is aborted. The error condition must be cleared with the SFLUSHTX strobe.
The TX_UNDERFLOW exception can be disabled by setting the FRMCTRL1.IGNORE_TX_UNDERF bit. In
this case, the CC2520 will continue transmitting the bytes that happen to be in the TX FIFO memory, until
the number of bytes given by the first byte (i.e. the length byte) has been transmitted
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