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LEN
LEN –2 Bytes
LEN
AUTOCRC
= 0
AUTOCRC
= 1
LEN –2 Bytes
FCS
(2 Bytes)
–
(Ignored)
–
(Ignored)
M0109-01
Transmit Mode
illustrates what must be written to the TXFIFO (marked blue). Additional bytes are ignored,
unless TX overflow occurs (see the error conditions listed in
Figure 23-5. Frame Data Written to the TXFIFO
There are two ways to write to the TXFIFO.
•
Write to the
RFD
register.
•
Frame buffering always begins at the start of the TXFIFO memory. By enabling the
FRMCTRL1.IGNORE_TX_UNDERF
bit, it is possible to write directly into the RAM area in the radio
memory, which holds the TXFIFO. Note that it is recommended to use the
RFD
register for writing data
to the TXFIFO.
The number of bytes in the TXFIFO is stored in the
TXFIFOCNT
register.
The TXFIFO can be emptied manually with the SFLUSHTX command strobe. TX underflow occurs if the
FIFO is emptied during transmission.
23.8.4 Retransmission
In order to support simple retransmission of frames, the radio does not delete the TXFIFO contents as
they are transmitted. After a frame has been successfully transmitted, the FIFO contents are left
unchanged. To retransmit the same frame, simply restart TX by issuing an STXON or STXONCCA
command strobe. Note that a retransmission of a packet is only possible if the packet has been completely
transmitted; i.e., a packet cannot be aborted and then be retransmitted.
If a different frame is to be transmitted, issue an ISFLUSHTX strobe and then write the new frame to the
TXFIFO.
23.8.5 Error Conditions
There are two error conditions associated with the TXFIFO:
•
Overflow happens when the TXFIFO is full and another byte write is attempted.
•
Underflow happens when the TXFIFO is empty and the radio attempts to fetch another byte for
transmission.
TX overflow is indicated by the TX_OVERFLOW interrupt flag being set. When this error occurs, the
writing is aborted, i.e., the data byte that caused the overflow is lost. The error condition must be cleared
with the SFLUSHTX strobe.
TX underflow is indicated by the TX_UNDERFLOW interrupt flag being set. 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 radio continues transmitting the bytes that happen to be in the TXFIFO memory, until the
number of bytes given by the first byte (i.e., the length byte) has been transmitted.
23.8.6 TX Flow Diagram
summarizes the previous sections in a flow diagram:
230
CC253x Radio
SWRU191C
–
April 2009
–
Revised January 2012
Copyright
©
2009
–
2012, Texas Instruments Incorporated