MC68HSC705C8ACFS datasheet(71/222 Pages) FREESCALE

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Low-Power Modes

Stop Mode

MC68HC705C8A — Rev. 3

Technical Data

MOTOROLA

Low-Power Modes

6.3.1 SCI During Stop Mode

When the MCU enters stop mode, the baud rate generator stops, halting

all SCI activity. If the STOP instruction is executed during a transmitter

transfer, that transfer is halted. If a low input to the IRQ pin is used to exit

stop mode, the transfer resumes.

If the SCI receiver is receiving data and stop mode is entered, received

data sampling stops because the baud rate generator stops, and all

subsequent data is lost. Therefore, all SCI transfers should be in the idle

state when the STOP instruction is executed.

6.3.2 SPI During Stop Mode

When the MCU enters stop mode, the baud rate generator stops,

terminating all master mode SPI operations. If the STOP instruction is

executed during an SPI transfer, that transfer halts until the MCU exits

stop mode by a low signal on the IRQ pin. If reset is used to exit stop

mode, the SPI control and status bits are cleared, and the SPI is

disabled.

If the MCU is in slave mode when the STOP instruction is executed, the

slave SPI continues to operate and can still accept data and clock

information in addition to transmitting its own data back to a master

device. At the end of a possible transmission with a slave SPI in stop

mode, no flags are set until a low on the IRQ pin wakes up the MCU.

NOTE:

Although a slave SPI in stop mode can exchange data with a master SPI,

the status bits of a slave SPI are inactive in stop mode.

6.3.3 Programmable COP Watchdog in Stop Mode

The STOP instruction turns off the internal oscillator and suspends the

computer operating properly (COP) watchdog counter. If the RESET pin

brings the MCU out of stop mode, the reset function clears and disables

the COP watchdog.

If the IRQ pin brings the MCU out of stop mode, the COP counter

resumes counting from its suspended value after the 4064-t

CYC clock

stabilization delay. See Figure 6-2.

Freescale Semiconductor, Inc.

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