ST72321AR STMICROELECTRONICS [STMicroelectronics], ST72321AR Datasheet - Page 45

• Manufacturer Part Number: ST72321AR
• Description: 64/44-PIN 8-BIT MCU WITH 32 TO 60K FLASH/ROM, ADC,FIVE TIMERS, SPI, SCI, I2C INTERFACE
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

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-
– The opcode for the HALT instruction is 0x8E. To
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.
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-
– As the HALT instruction clears the interrupt mask
Related Documentation
AN 980: ST7 Keypad Decoding Techniques, Im-
plementing Wake-Up on Keystroke
AN1014: How to Minimize the ST7 Power Con-
sumption
AN1605: Using an active RC to wakeup the
ST7LITE0 from power saving mode
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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