MC68HC908AP16CFB datasheet(304/440 Pages) MOTOROLA

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Serial Peripheral Interface Module (SPI)

Data Sheet

MC68HC908AP Family — Rev. 2.5

304

MOTOROLA

MODF generates a receiver/error CPU interrupt request if the error

interrupt enable bit (ERRIE) is also set. The SPRF, MODF, and OVRF

interrupts share the same CPU interrupt vector. (See Figure 15-11.) It is

not possible to enable MODF or OVRF individually to generate a

receiver/error CPU interrupt request. However, leaving MODFEN low

prevents MODF from being set.

In a master SPI with the mode fault enable bit (MODFEN) set, the mode

fault flag (MODF) is set if SS goes to logic 0. A mode fault in a master

SPI causes the following events to occur:

•

If ERRIE = 1, the SPI generates an SPI receiver/error CPU

interrupt request.

•

The SPE bit is cleared.

•

The SPTE bit is set.

•

The SPI state counter is cleared.

•

The data direction register of the shared I/O port regains control of

port drivers.

NOTE:

To prevent bus contention with another master SPI after a mode fault

error, clear all SPI bits of the data direction register of the shared I/O port

before enabling the SPI.

When configured as a slave (SPMSTR = 0), the MODF flag is set if SS

goes high during a transmission. When CPHA = 0, a transmission begins

when SS goes low and ends once the incoming SPSCK goes back to its

idle level following the shift of the eighth data bit. When CPHA = 1, the

transmission begins when the SPSCK leaves its idle level and SS is

already low. The transmission continues until the SPSCK returns to its

idle level following the shift of the last data bit. (See 15.5 Transmission

Formats.)

NOTE:

Setting the MODF flag does not clear the SPMSTR bit. The SPMSTR bit

has no function when SPE = 0. Reading SPMSTR when MODF = 1

shows the difference between a MODF occurring when the SPI is a

master and when it is a slave.

When CPHA = 0, a MODF occurs if a slave is selected (SS is at logic 0)

and later unselected (SS is at logic 1) even if no SPSCK is sent to that

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

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