NXP Semiconductors MPC5566, Reference Manual

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Deserial Serial Peripheral Interface (DSPI)
MPC5566 Microcontroller Reference Manual, Rev. 2
Freescale Semiconductor 20-71
Figure 20-43 illustrates the concept of first-in and last-in FIFO entries along with the FIFO counter.
Figure 20-43. TX FIFO Pointers and Counter
20.5.5.1 Address Calculation for the First-in Entry and Last-in
Entry in the TX FIFO
The memory address of the first-in entry in the TX FIFO is computed by the following equation:
First-in entry address = TXFIFO base + 4 (TXNXTPTR)
The memory address of the last-in entry in the TX FIFO is computed by the following equation:
Last-in entry address = TXFIFO base + (4
x
[(TXCTR + TXNXTPTR - 1) modulo TXFIFO depth])
where:
TXFIFO base = base address of transmit FIFO
TXCTR = transmit FIFO counter
TXNXTPTR = transmit next pointer
TX FIFO depth = transmit FIFO depth, implementation specific
20.5.5.2 Address Calculation for the
First-in Entry and Last-in Entry in the RX FIFO
The memory address of the first-in entry in the RX FIFO is computed by the following equation:
First-in entry address = RXFIFO base + 4
x
(POPNXTPTR)
The memory address of the last-in entry in the RX FIFO is computed by the following equation:
Last-in entry address = RXFIFO base + 4
x
[(RXCTR + POPNXTPTR - 1) modulo RXFIFO depth]
where:
RXFIFO base = base address of receive FIFO
RXCTR = receive FIFO counter
POPNXTPTR = pop next pointer
RX FIFO depth = receive FIFO depth, implementation specific
Entry C
Entry A (first in)
– 1
Entry B
Entry D (last in)
TX FIFO base
Push TX FIFO
TX FIFO counter
Shift register SOUT
register
Transmit next
data pointer
–
–
–
–
+ 1
(TXNXTPTR)