PXN20RM Datasheet, PDF (989/1376 Pages) Freescale Semiconductor, Inc – PXN20 Microcontroller

Deserial – Serial Peripheral Interface (DSPI)
30.5.5.1 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 = TX FIFO Base + 4  TXNXTPTR
Eqn. 30-10
The memory address of the last-in entry in the TX FIFO is computed by the following equation:
Last-in Entry address = TX FIFO Base + 4  modulo TX FIFO depthTXCTR + TXNXTPTR – 1
where:
TX FIFO base: base address of TX FIFO
TXCTR: TX FIFO counter
TXNXTPTR: transmit next pointer
TX FIFO depth: transmit FIFO depth
Eqn. 30-11
30.5.5.2 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 = RX FIFO Base + 4  POPNXTPTR
Eqn. 30-12
The memory address of the last-in entry in the RX FIFO is computed by the following equation:
Last-in Entry address = RX FIFO Base + 4  modulo RX FIFO depthRXCTR + POPNXTPTR – 1
where:
RX FIFO base: base address of RX FIFO
RXCTR: RX FIFO counter
POPNXTPTR: pop next pointer
RX FIFO depth: receive FIFO depth
Eqn. 30-13
Freescale Semiconductor
PXN20 Microcontroller Reference Manual, Rev. 1
30-63