MSC8144E Reference Manual, Rev. 3
18-42
Freescale
Semiconductor
QUICC Engine™ Subsystem
To start exchanging data, the QUICC Engine subsystem writes the data to be sent into a buffer,
configures a TxBD with TxBD[R] set, and configures one or more RxBDs. The QUICC Engine
subsystem 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 SPI_CK for each character and
simultaneously shifts Tx data out on SPI_MOSI and Rx data in on SPI_MISO. 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 QUICC Engine subsystem then
clears TxBD[R] and RxBD[E] and issues a maskable interrupt to the interrupt controller.
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 SPI_MOSI
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.
Figure 18-22. Single-Master/Multi-Slave Configuration
SPI_MOSI
SPI_MISO
SPI_CK
SPI_SL
Slave 0
SPI_MISO
SPI_CK
SPI_SL
Slave 1
Slave 2
Master SPI
SPI_MOSI
SPI_MISO
SPI_CK
SPI_SL
SPI_MOSI
SPI_SL
SPI_CK
SPI_MISO
SPI_MOSI
Decoder can be
Either Internal or
External Logic
Содержание MSC8144E
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