ST6369 datasheet(25/71 Pages) STMICROELECTRONICS

25 / 71 page

WAIT & STOP MODES

The STOP and WAIT modes have been imple-

mented in the ST6369 Core in order to reduce the

consumption of the device when the latter has no

instruction to execute. These two modes are de-

scribed in the following paragraphs. On ST6369 as

the hardware activated digital watchdog function is

present the STOP instruction is de-activated and

any attempt to execute it will cause the automatic

execution of a WAIT instruction.

WAIT Mode

The configuration of the MCU in the WAIT mode oc-

curs as soon as the WAIT instruction is executed.

The microcontroller can also be considered as being

in a “software frozen” state where the Core stops

processing the instructions of the routine, the con-

tents of the RAM locations and peripheral registers

are saved as long as the power supply voltage is

higher than the RAM retention voltage but where the

peripherals are still working.

The WAIT mode is used when the user wants to

reduce the consumption of the MCU when it is in

idle, while not losing count of time or monitoring of

external events. The oscillator is not stopped in

order to provide clock signal to the peripherals.

The timers counting may be enabled (writing the

PSI bit in TSCR register) and the timer interrupt

may be also enabled before entering the WAIT

mode; this allows the WAIT mode to be left when

timer interrupt occurs. If the exit from the WAIT

mode is performed with a genera l RESET (either

from the activation of the external pin or by watch-

dog reset) the MCU will enter a normal reset pro-

cedure as described in the RESET chapter. If an

interrupt is generated during WAIT mode the

MCU behaviour depends on the state of the

ST6369 Core before the initialization of the WAIT

sequence, but also of the kind of the interrupt re-

quest that is generated. This case will be de-

scribed in the following paragraphs. In any case,

the ST6369 Core does not genera te any delay af-

ter the occurrence of the interrupt because the

oscillator clock is still available.

STOP Mode

On ST6369 the hardware watchdog is present and

the STOP instruction has been de-activated. Any

attempt to execute a STOP will cause the auto-

matic execution of a WAIT instruction.

Exit from WAIT Mode

The following paragraphs describe the output pro-

cedure of the ST6369 Core from WAIT mode when

an interrupt occurs. It must be noted that the restart

sequence depends on the original state of the

MCU (normal, interrupt or non-maskable interrupt

mode) before the start of the WAIT sequence, but

also of the type of the interrupt request that is gen-

erated. In all cases the GEN bit of IOR has to be set

to 1 in order to restart from WAIT mode. Contrary

to the operation of NMI in the run mode, the NMI is

masked in WAIT mode if GEN=0.

Normal Mode. If the ST6369Corewas in themain

routinewhen the WAIT instruction has been executed,

the ST6369 Core outputsfrom the wait mode as soon

as any interrupt occurs; the related interrupt routine is

executedand at the end of the interruptservice routine

the instruction that follows the WAIT instruction is exe-

cuted if no other interrupts are pending.

Non-maskable Interrupt Mode. If the WAIT in-

struction has been executed during the execution

of the non-maskable interrupt routine, the ST6369

Core outputs from the wait mode as soon as any

interrupt occurs: the instruction that follows the

WAIT instruction is executed and the ST6369 Core

is still in the non-maskable interrupt mode even if

another interrupt has been generated.

Normal Interrupt Mode. If the ST6369 Core was

in the interrupt mode before the initialization of the

WAIT sequence, it outputs from the wait mode as

soon as any interrupt occurs. Nevertheless, two

cases have to be considered:

–

If the interrupt is a normal interrupt, the inter-

rupt routine in which the WAIT was entered

will be completed with the execution of the in-

struction that follows the WAIT and the

ST6369 Core is still in the interrupt mode. At

the end of this routine pending interrupts will

be serviced in accordance to their priority.

–

If the interrupt is a non-maskable interrupt,

the non-maskable routine is processed at

first. Then, the routine in which the WAIT was

entered will be completed with the execution

of the instruction that follows the WAIT and

the ST6369 Core is still in the normal inter-

rupt mode.

Notes :

If all the interrupt sources are disabled, the restart

of the MCU can only be done by a Reset activation.

The Wait instruction is not executed if an enabled

interrupt request is pending. In the ST6369 the

hardware activated digital watchdog function is

present. As the watchdog is always activated the

STOP instruction is de-activated and any attempt

to execute the STOP instruction will cause an exe-

cution of a WAIT instruction.

ST6369

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