ST7263BEx datasheet(56/186 Pages) STMICROELECTRONICS

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On-chip peripherals

ST7263Bxx

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Doc ID 7516 Rev 8

HALT instruction

If the Watchdog reset on HALT option is selected by option byte, a HALT instruction causes

an immediate reset generation if the Watchdog is activated (WDGA bit is set).

Using Halt mode with the WDG (option)

If the Watchdog reset on HALT option is not selected by option byte, the Halt mode can be

used when the watchdog is enabled.

In this case, the HALT instruction stops the oscillator. When the oscillator is stopped, the

WDG stops counting and is no longer able to generate a reset until the microcontroller

receives an external interrupt or a reset.

If an external interrupt is received, the WDG restarts counting after 4096 CPU clocks. If a

reset is generated, the WDG is disabled (reset state).

Recommendations:

●

Make sure that an external event is available to wake up the microcontroller from Halt

mode.

●

Before executing the HALT instruction, refresh the WDG counter, to avoid an

unexpected WDG reset immediately after waking up the microcontroller.

●

When using an external interrupt to wake up the 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

external interference or by an unforeseen logical condition.

●

For the same reason, reinitialize the level sensitiveness of each external interrupt as a

precautionary measure.

●

The opcode for the HALT instruction is 0x8E. To avoid an unexpected HALT instruction

due to a program counter failure, it is advised to clear all occurrences of the data value

0x8E from memory. For example, avoid defining a constant in ROM with the value

0x8E.

●

As the HALT instruction clears the I bit in the CC register to allow interrupts, the user

may choose to clear all pending interrupt bits before executing the HALT instruction.

This avoids entering other peripheral interrupt routines after executing the external

interrupt routine corresponding to the wakeup event (reset or external interrupt).

11.1.7

Interrupts

None.

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