W79E225A_08 Datasheet, PDF (172/203 Pages) Winbond – 8-bit Microcontroller

Preliminary W79E225A/226A/227A Data Sheet
Figure 18-11: SPI Overrun Timing Waveform
18.3.8 LSB first enable
By default, this device transfer the SPI data most significant bit first. This device provides a control bit
SPCR.LSBFE to allow support of transfer of SPI data in least significant bit first.
18.3.9 Write Collision detection
Write collision indicates that an attempt was made to write data to the SPDR while a transfer was in
progress. SPDR is not double buffered in the transmit direction, any writes to SPDR cause data to be
written directly into the SPI shift register. This write corrupts any transfer in progress, a write collision
error is generated (WCOL will be set). The transfer continues undisturbed, and the write data that
caused the error is not written to the shifter. A write collision is normally a slave error because a slave
has no control over when a master initiates a transfer. A master knows when a transfer is in progress,
so there is no reason for a master to generate a write-collision error, although the SPI logic can detect
write collisions in both master and slave devices. WCOL flag is clear by software.
18.3.10Transfer complete interrupt
This device consists of an interrupt flag at SPIF. This flag will be set upon completion of data transfer
with external device, or when a new data have been received and copied to SPDR. If interrupt is
enable (through ESPI), the SPI interrupt request will be generated, if global enable bit EA is also
enabled. SPIF is software clear.
18.3.11Mode Fault
Error arises in a multiple-master system when more than one SPI device simultaneously tries to be a
master. This error is called a mode fault.
When the SPI system is configured as a master and the /SS input line goes to active low, a mode fault
error has occurred — usually because two devices have attempted to act as master at the same time.
In cases where more than one device is concurrently configured as a master, there is a chance of
contention between two pin drivers. For push-pull CMOS drivers, this contention can cause permanent
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Publication Release Date: April 15, 2008
Revision A4.0