SX1231
ADVANCED COMMUNICATIONS & SENSING
DATASHEET
The frame ends when NSS goes high. The next frame must start with an address byte. The SINGLE access mode is
actually a special case of FIFO / BURST mode with only 1 data byte transferred.
During the write access, the byte transferred from the slave to the master on the MISO line is the value of the written
register before the write operation.
5.2.2. FIFO
5.2.2.1. Overview and Shift Register (SR)
In packet mode of operation, both data to be transmitted and that has been received are stored in a configurable FIFO
(First In First Out) device. It is accessed via the SPI interface and provides several interrupts for transfer management.
The FIFO is 1 byte wide hence it only performs byte (parallel) operations, whereas the demodulator functions serially. A
shift register is therefore employed to interface the two devices. In transmit mode it takes bytes from the FIFO and outputs
them serially (MSB first) at the programmed bit rate to the modulator. Similarly, in Rx the shift register gets bit by bit data
from the demodulator and writes them byte by byte to the FIFO. This is illustrated in figure below.
FIFO
byte1
byte0
8
Data Tx/Rx
SR (8bits)
1
MSB
LSB
Figure 23. FIFO and Shift Register (SR)
Note When switching to Sleep mode, the FIFO can only be used once the ModeReady flag is set (quasi immediate from
all modes except from Tx)
5.2.2.2. Size
The FIFO size is fixed to 66 bytes.
5.2.2.3. Interrupt Sources and Flags
FifoNotEmpty: FifoNotEmpty interrupt source is low when byte 0, i.e. whole FIFO, is empty. Otherwise it is high. Note
that when retrieving data from the FIFO, FifoNotEmpty is updated on NSS falling edge, i.e. when FifoNotEmpty is
updated to low state the currently started read operation must be completed. In other words, FifoNotEmpty state must
be checked after each read operation for a decision on the next one (FifoNotEmpty = 1: more byte(s) to read;
FifoNotEmpty = 0: no more byte to read).
FifoFull: FifoFull interrupt source is high when the last FIFO byte, i.e. the whole FIFO, is full. Otherwise it is low.
FifoOverrunFlag: FifoOverrunFlag is set when a new byte is written by the user (in Tx or Standby modes) or the SR (in
Rx mode) while the FIFO is already full. Data is lost and the flag should be cleared by writing a 1, note that the FIFO will
also be cleared.
PacketSent: PacketSent interrupt source goes high when the SR's last bit has been sent.
FifoLevel: Threshold can be programmed by FifoThreshold in RegFifoThresh. Its behavior is illustrated in figure below.
Rev 2 - Nov 2009
Page 43
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