ST72F321J ST Microelectronics, ST72F321J Datasheet - Page 43

• Manufacturer Part Number: ST72F321J
• Description: 8-BIT MCU
• Manufacturer: ST Microelectronics

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DataSheet
POWER SAVING MODES (Cont’d)
8.4.2.1 Halt Mode Recommendations
– Make sure that an external event is available to
– When using an external interrupt to wake up the
– For the same reason, reinitialize the level sensi-
wake up the microcontroller from Halt mode.
microcontroller, reinitialize the corresponding I/O
as “Input Pull-up with Interrupt” before executing
the HALT instruction. The main reason for this is
that the I/O may be wrongly configured due to ex-
ternal interference or by an unforeseen logical
condition.
tiveness of each external interrupt as a precau-
tionary measure.
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– The opcode for the HALT instruction is 0x8E. To
– As the HALT instruction clears the interrupt mask
avoid an unexpected HALT instruction due to a
program counter failure, it is advised to clear all
occurrences of the data value 0x8E from memo-
ry. For example, avoid defining a constant in
ROM with the value 0x8E.
in the CC register to allow interrupts, the user
may choose to clear all pending interrupt bits be-
fore executing the HALT instruction. This avoids
entering other peripheral interrupt routines after
executing the external interrupt routine corre-
sponding to the wake-up event (reset or external
interrupt).
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