L9805 datasheet(25/103 Pages) STMICROELECTRONICS

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L9805

POWER SAVING MODES (Cont’d)

3.7.4 Halt Mode

The Halt mode is the MCU lowest power con-

sumption mode. The Halt mode is entered by exe-

cuting the HALT instruction. The internal oscillator

is then turned off, causing all internal processing to

be stopped, including the operation of the on-chip

peripherals.

When entering Halt mode, the I bit in the CC Reg-

ister is cleared so as to enable External Interrupts.

If an interrupt occurs, the CPU becomes active.

The MCU can exit the Halt mode upon reception of

either an external interrupt (I0), a internal interrupt

coming from the CAN peripheral (I1) or a reset.

The oscillator is then turned on and a stabilisation

time is provided before releasing CPU operation.

The stabilisation time is 4096 CPU clock cycles.

After the start up delay, the CPU continues opera-

tion by servicing the interrupt which wakes it up or

by fetching the reset vector if a reset wakes it up.

Note The Halt mode cannot be used when the

watchdog or the Safeguard are enabled, if the

HALT instruction is executed while the watchdog

or safeguard system are enabled, a reset is auto-

matically generated thus resetting the entire MCU.

Note Halt Mode affects only the digital section of

the device. All the analog circuit remain in their

status, including ADC, voltage regulators, bus

transceivers and power bridge.

Figure 13. Halt Mode Flow Chart

EXTERNAL

INTERRUPT

RESET

HALT INSTRUCTION

4096 CPU CLOCK

FETCH RESET VECTOR

OR SERVICE INTERRUPT

CYCLES DELAY

CPU CLOCK

OSCILLATOR

PERIPH. CLOCK

I-BIT

SET

CPU CLOCK

OSCILLATOR

PERIPH. CLOCK

I-BIT

OFF

CLEARED

OFF

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