ST52T400 datasheet(44/94 Pages) STMICROELECTRONICS

44 / 94 page

ST52T400/T440/E440/T441

44/94

5.2.4 Brown-Out Detector (BOD).

The on-chip Brown-Out Detector circuit prevents

the processor from falling into an unpredictable

state if the power supply drops below a certain

level.

When Vdd drops below the Brown-out detection

level, the Brown-out causes an internal proces-

sor reset RST that remains active as long as Vdd

remains below the Brown-Out Trigger Level.

Brown-Out resets the entire device except the

Power-on Detector and the Brown-out itself.

Enabling/disabling the Brown-out detector can be

performed by setting the software of the control bit

BOD of REG_CONF0 (Table 4.1).

When Vdd increases above the Trigger Level, the

Brown-Out reset is turned off after a delay of 4096

CPU clock cycles, which ensures stabilization of

the oscillator.

The Brown-Out falling voltage level typical value is

3.8V and the corresponding rising voltage activa-

tion level is 4.1V.

A minimum hysteresis of 250mV for the trigger is

guaranteed for spike free brown-out detection.

Brown-Out circuit detects a drop if Vdd voltage

stays below the safe threshold for longer than 100

Clock cycles before activation/deactivation of the

Brown-Out in order to filter voltage spikes.

Brown-Out function is disabled by default and is

not active when in HALT mode.

Remark:

for higher frequencies, the device needs

Supply Voltage higher than the BOD threshold.

For this reason the BOD cannot work in this range

frequencies.

See

Electrical

Characteristic

Chapter in this Datasheet.

5.3 Power Saving Modes

There are two Power Saving modes: WAIT and

HALT mode. These conditions may be entered by

using the WAIT and HALT instructions.

5.3.1 Wait Mode.

Wait mode places the MCU in a low power con-

sumption by stopping the CPU. All peripherals and

the watchdog remain active. During WAIT mode,

the Interrupts are enabled. The MCU will remain in

Wait mode until an Interrupt or a RESET occurs,

whereupon the Program jumps to the interrupt

service routine or, if a RESET occurs, at the

beginning of the user program.

Remark:

in Wait mode the CPU clock does’t stop.

5.3.2 Halt Mode.

Halt mode is the MCU’s lowest power consump-

tion mode, which is entered by executing the

HALT instruction. The internal oscillator is turned

off, causing all internal processing to be stopped,

including the operations of the on-chip peripher-

als.

Halt mode cannot be used when the watchdog

is enabled. If the HALT instruction is executed

while the watchdog system is enabled, it will be

skipped without modifying the normal CPU opera-

tions.

TheICU canexit Halt modeafter anexternal inter-

rupt or reset. The oscillator is then turned on and

stabilization time is provided before restarting

CPU operations. Stabilization time is 4096 CPU

clock cycles after the interrupt and 1.000.000 after

the Reset.

After the start up delay, the CPU restarts opera-

tions by serving the external interrupt routine.

Reset makes the ICU exit from HALT mode and

restart, after the delay, from the beginning of the

user program after the delay.

Warning:

if the External Interrupt is disabled, the

ICU exits from the Halt mode and jumps to the

lower priority interrupt routine.

Figure 5.3 WAIT Flow Chart

ST52T400 数据表(PDF) 44 Page - STMicroelectronics

ST52T400 数据表(HTML) 44 Page - STMicroelectronics

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94

数据表下载