ST72621L4M1(2002) View Datasheet(PDF) - STMicroelectronics

Part Name

Description

Manufacturer

ST72621L4M1
(Rev.:2002)

LOW SPEED USB 8-BIT MCU WITH 3 ENDPOINTS, FLASH OR ROM MEMORY, LVD, WDG, 10-BIT ADC, 2 TIMERS, SCI, SPI

STMicroelectronics 

ST7262

POWER SAVING MODES (Cont’d)

Figure 25. HALT Mode Flow Chart

8.3 HALT MODE

The HALT mode is the MCU lowest power con-

sumption mode. The HALT mode is entered by ex-

ecuting the HALT instruction. The internal oscilla-

tor is then turned off, causing all internal process-

ing to be stopped, including the operation of the

on-chip peripherals.

When entering HALT mode, the I bit in the Condi-

tion Code Register is cleared. Thus, any of the ex-

ternal interrupts (ITi or USB end suspend mode),

are allowed and if an interrupt occurs, the CPU

clock becomes active.

The MCU can exit HALT mode on reception of ei-

ther an external interrupt on ITi, an end suspend

mode interrupt coming from USB peripheral, or a

reset. The oscillator is then turned on and a stabi-

lization time is provided before releasing CPU op-

eration. The stabilization time is 514 CPU clock cy-

cles.

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.

HALT INSTRUCTION

OSCILLATOR

PERIPH. CLOCK

CPU CLOCK

I-BIT

OFF

OFF

OFF

CLEARED

N

N

EXTERNAL

INTERRUPT*

RESET

Y

Y

OSCILLATOR

PERIPH. CLOCK

CPU CLOCK

I-BIT

ON

ON

ON

SET

514 CPU CLOCK

CYCLES DELAY

FETCH RESET VECTOR

OR SERVICE INTERRUPT

Note: Before servicing an interrupt, the CC register is

pushed on the stack. The I-Bit is set during the inter-

rupt routine and cleared when the CC register is

popped.

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