MPC8280 datasheet(1287/1386 Pages) FREESCALE

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Serial Peripheral Interface (SPI)

MPC8280 PowerQUICC II Family Reference Manual, Rev. 1

Freescale Semiconductor

39-3

39.3.1

The SPI as a Master Device

In master mode, the SPI sends a message to the slave peripheral, which sends back a simultaneous reply.

A single master MPC8280 with multiple slaves can use general-purpose parallel I/O signals to selectively

enable slaves, as shown in Figure 39-2. To eliminate the multimaster error in a single-master environment,

the master’s SPISEL input can be forced inactive by selecting port D[19] for general-purpose I/O

(PDPAR[DD19] = 0).

Figure 39-2. Single-Master/Multi-Slave Configuration

To start exchanging data, the core writes the data to be sent into a buffer, configures a TxBD with TxBD[R]

set, and configures one or more RxBDs. The core then sets SPCOM[STR] in the SPI command register to

start sending data, which starts once the SDMA channel loads the Tx FIFO with data.

The SPI then generates programmable clock pulses on SPICLK for each character and simultaneously

shifts Tx data out on SPIMOSI and Rx data in on SPIMISO. Received data is written into a Rx buffer using

the next available RxBD. The SPI keeps sending and receiving characters until the whole buffer is sent or

an error occurs. The CP then clears TxBD[R] and RxBD[E] and issues a maskable interrupt to the interrupt

controller in the SIU.

When multiple TxBDs are ready, TxBD[L] determines whether the SPI keeps transmitting without

SPCOM[STR] being set again. If the current TxBD[L] is cleared, the next TxBD is processed after data

from the current buffer is sent. Typically there is no delay on SPIMOSI between buffers. If the current

TxBD[L] is set, sending stops after the current buffer is sent. In addition, the RxBD is closed after

transmission stops, even if the Rx buffer is not full; therefore, Rx buffers need not be the same length as

Tx buffers.

SPIMOSI

SPIMISO

SPICLK

SPISEL

Slave 0

SPIMISO

SPICLK

SPISEL

Slave 1

Slave 2

Master SPI

SPIMOSI

SPIMISO

SPICLK

SPISEL

SPIMOSI

The SPISEL

SPICLK

SPIMISO

SPIMOSI

MPC8280

decoder can be

either internal or

external logic.

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