Serial Peripheral Interface Controller
UG0331 User Guide Revision 15.0
510
falling edge at the end of the transmission. This means that SPI_X_DOE_N must be held High for at
least one half SPI_X_CLK after the last falling edge to satisfy the hold time requirement.
14.2.2.3.3 Motorola SPI Error Case Scenarios
The SPI protocol does not specify any error recovery strategy. The master and slave require prior
knowledge of clock rates and data-frame layouts. However, there are built-in mechanisms in the SPI
controller to recover from error. If the slave encounters an error, the master can toggle the slave clock
until it comes to a known state. Here are three specific scenarios and error the behavior of the SPI
controller in Motorola protocol mode.
•
If the slave select signal is withdrawn in the middle of a transfer, the transfer continues until the end
of the data frame.
•
If the input clock is withdrawn, the SPI controller remains paused until the clock is restarted. It picks-
up where it left off.
•
If the slave select signal is withdrawn before a transfer occurs, the slave remains in the idle state (no
data transfer having been initiated).
The SPI controller has no built-in timer. For applications where there is a possibility of a slave going to
sleep for a long time, or in the case of very long transfers, the application should use a timer created from
user logic.
14.2.2.3.4 SPI Data Transfer for Large Flash/EEPROM Devices in Motorola SPI Modes
Serial flash and EEPROM devices can be driven using Motorola SPI modes. Following is an outline of
the interfaces to the required flash/EEPROM devices that shows how they can be driven using Motorola
SPI modes. In each of these modes, the SPI controller is configured as a master with the slave select line
connected to the chip select of the memory device.
Devices Requiring Data Frame Sizes of Up to 32 Bits
Serial flash/EEPROM devices, such as the Atmel 25010/020/040, have a data frame size smaller than 32
bits and can be directly driven from SPI mode.
Write Operation for Atmel 25010/020/040 Devices
Table 495 •
Behavior of the Output Enable Signal
Mode
Master
Slave
MOTOROLA
SPI_X_DOE_N is asserted with identical timing
to that of SPI_X_SS[0]. This provides an
additional half SPI_X_CLK cycle of data turn on
and off relative to the data bit valid
requirements.
The incoming SPI_X_SS[0] signal is used to
directly generate the SPI_X_DOE_N. Similar to the
master case, it provides an additional half clock
cycle of data turn on and off.
Texas
Instruments
SPI_X_DOE_N is asserted on the negative
clock edge prior to the MSB (while SPI_X_SS[0]
is asserted) and if the uninterrupted data is
deasserted on the falling SPI_X_CLK edge
following the LSB. This provides half a clock
cycle of data turn on off time.
SPI_X_DOE_N is asserted on the positive SPI
clock edge as the MSB is the output.
SPI_X_DOE_N is deasserted on the positive SPI
clock edge at the end of the LSB data bit,
assuming no consecutive data.
National
Semiconductor
MICROWIRE
SPI_X_DOE_N is asserted with SPI_X_SS[0],
and then removed at the start of the ninth data
bit (turn around cycle).
SPI_X_DOE_N is asserted at the start of the tenth
bit as data becomes valid. SPI_X_DOE_N is
deasserted at the end of the LSB, if a falling clock
edge occurs or when SPI_X_SS[0] is deasserted.
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