Serial Peripheral Interface Controller
UG0331 User Guide Revision 15.0
514
14.2.2.5 Texas Instruments Synchronous Serial Protocol
The Texas Instruments (TI) synchronous serial interface is based on a full duplex, four-wire synchronous
transfer protocol. The transmit data pin is put in a high-impedance mode (tristated) when no data is
transmitted.
•
The slave select (SPI_X_SS[x]) signal is pulsed between transfers to guarantee a high-to-low
transition between each frame.
•
The slave select output polarity is inverted to become active High. In an idle state, the slave select
(SPI_X_SS[x]) signal is kept low.
•
Data is available on the clock cycle immediately following the slave select (SPI_X_SS[x]) assertion.
•
Both the SPI master and the SPI slave capture each data bit into their serial shift registers on the
falling edge of the clock (SPI_X_CLK). The received data is latched on the rising edge of the clock
(SPI_X_CLK).
•
The output enable signal (SPI_X_DOE_N) is asserted (active Low) throughout the transfer.
The following figures show the TI synchronous single frame transfer and TI synchronous multiple frame
transfer.
Figure 216 •
TI Synchronous Serial Single Frame Transfer
Figure 217 •
TI Synchronous Serial Multiple Frame Transfer
14.2.2.5.1 TI Synchronous Serial Error Case Scenarios
When the SPI controller is configured for the TI synchronous serial protocol, while in slave mode, it
responds to failure events. These failure events on slave select (SPI_X_SS[x]) and the slave clock
(SPI_X_CLK) are described below:
•
Withdrawal of SPI_X_CLK: In this case, the device pauses and resumes on reasserting the clock.
•
Premature pulsing of slave select: If the slave select is pulsed during a data frame transmission, it
will be ignored.
•
Disconnecting the slave select before a transfer: The transfer is not initiated unless the pulse is
issued.
14.2.2.6 Slave Protocol Engine
The slave protocol engine (SPE) implements a Microsemi-defined hardware protocol that allows the
transfer of command and data from an SPI master to the SPI slave. The SPE controller logically sits
between the SPI transmit/receive logic and the FIFOs. The SPE controller removes the command bytes
and inserts status bytes from the data stream. Only one command byte is defined by Microsemi
4 to 16 Bits
SPI_CLK
SPI_DI
SPI_DOE_N
SPI_DO
SPI_SS[x]
LSB
MSB
4 to 16 Bits
SPI_CLK
SPI_DI
SPI_DOE_N
SPI_DO
SPI_SS[x]
LSB
MSB
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