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There is one way to wake from stop mode via the SPI, which is explained in the
following section.
3.9.3.7.1 Using GPIO Interrupt to Wake from stop mode
Here are the steps to use a GPIO to create a wakeup upon reception of SPI data in slave
mode:
1. Point the GPIO interrupt vector to the desired interrupt handler.
2. Enable the GPIO input to generate an interrupt on either the rising or falling edge
(depending on the polarity of the chip select signal).
3. Enter Stop or VLPS mode and Wait for the GPIO interrupt.
NOTE
It is likely that in using this approach the first word of data from
the SPI host might not be received correctly. This is dependent
on the transfer rate used for the SPI, the delay between chip
select assertion and presentation of data, and the system
interrupt latency.
3.9.3.8 SPI Doze Mode
The Doze mode for the SPI module is the same as the Wait and VLPW modes for the
chip.
3.9.3.9 SPI Interrupts
The SPI has multiple sources of interrupt requests. However, these sources are OR'd
together to generate a single interrupt request per SPI module to the interrupt controller.
When an SPI interrupt occurs, read the SPI_SR to determine the exact interrupt source.
3.9.3.10 SPI clocks
This table shows the SPI module clocks and the corresponding chip clocks.
Table 3-63. SPI clock connections
Module clock Chip clock
System Clock Bus Clock
Chapter 3 Chip Configuration
K20 Sub-Family Reference Manual, Rev. 1.1, Dec 2012
Freescale Semiconductor, Inc.
Preliminary
137
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