NXP Semiconductors freescale semiconductor MC13211, Справочное руководство

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MC1321x Serial Peripheral Interface (SPI)
MC1321x Reference Manual, Rev. 1.6
Freescale Semiconductor 4-17
4.10 Modem Symbol/Data Format
When the modem transceiver receives 802.15.4 symbols, they are assembled as 4 symbols per 16-bit word.
They are then presented to the RX Packet RAM or to the SPI directly as a 16-bit word. The ordering of
symbols vs. word bit ordering is shown in
Figure 4-15 which details the RX data flow through the device.
In Packet Mode the data is loaded into RX Packet RAM, and in Stream Mode the data is sent directly to
the SPI buffer. When the symbols are read via the SPI bus, 2 SPI bursts per 16-bit word are required and
the MSB is presented first such that the symbols appear to the MCU in reverse order.
Figure 4-15. RX Symbol Flow Diagram
The inverse of the RX symbol / data flow is the case for TX data / symbols.
MISO
3
2
1
0
3
2
1
0
4th
Symbol
Received
3rd
Symbol
Received
3
2
1
0
3
2
1
0
2nd
Symbol
Received
1st
Symbol
Received
3
2
1
0
3
2
1
0
3
2
1
0
3
2
1
0 LSB
MSB
Symbol 1
Symbol 2
Symbol 3
Symbol 4
Symbol 1 Symbol 2 Symbol 3 Symbol 4
LSB
MSB
0 1 2 3 0 1 2 3 0 1 2 3 0 1 2 3
Symbol 1 Symbol 2 Symbol 3 Symbol 4
RX Packet RAM
LSB
MSB
0 1 2 3 0 1 2 3 0 1 2 3 0 1 2 3
Symbol 1 Symbol 2 Symbol 3 Symbol 4
MCU SPI
RX Stream Mode