HT95R22 datasheet(29/52 Pages) HOLTEK

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HT95R22

Rev. 1.00

January 6, 2009

Idle Mode

When the device enters this mode, the normal operating

current, will be reduced to an extremely low standby cur-

rent level. This occurs because when the device enters

the Power Down Mode, both the 3.58MHz and 32768Hz

system oscillators are stopped which reduces the power

consumption to extremely low levels, however, as the

device maintains its present internal condition, it can be

woken up at a later stage and continue running, without

requiring a full reset. This feature is extremely important

in application areas where the microcontroller must

have its power supply constantly maintained to keep the

device in a known condition but where the power supply

capacity is limited such as in battery applications.

Sleep Mode

In the Sleep Mode is similar to the mode, except here

the 32768Hz oscillator continues running after after the

HALT instruction has been executed. This feature en-

ables the device to continue with instruction execution

immediately after wake-up.

Green Mode

In the Green Mode, the 32768Hz oscillator is used as

the system clock for instruction execution. The following

conditions will force the microcontroller enter the Green

Mode:

· Any reset condition from any operational mode

· Any interrupt occurring during the Sleep Mode or Idle

mode

· A Port A Wake-up from the Sleep Mode or Idle Mode

Normal Mode

In the Normal mode the device uses the 3.58MHz gen-

erated by the frequency-up conversion circuit as the

system clock for instruction execution.

Changing the Operational Mode

Holtek

¢s telephone controllers support two system

clocks and four operational modes. The system clock

can be either 32768Hz or 3.58MHz and the operational

mode can be either Normal, Green, Sleep or Idle mode.

The operation mode is selected using software in the

following way:

· Normal mode to Green mode:

Clear bit MODE1 to 0, which will change the opera-

tional mode to the Green mode.

The UPEN bit status is not changed. However, the

UPEN bit can be cleared by software.

· Normal mode or Green mode to Sleep mode:

Step 1: Clear bit MODE0 to 0

Step 2: Clear bit MODE1 to 0

Step 3: Clear bit UPEN to 0

Step 4: Execute the HALT instruction

After Step 4, the operational mode will be changed to

the Sleep mode.

· Normal mode or Green mode to Idle mode:

Step 1: Set bit MODE0 to 1

Step 2: Clear bit MODE1 to 0

Step 3: Clear bit UPEN to 0

Step 4: Execute the HALT instruction

After Step 4, the operational mode will be changed to

the Idle mode.

· Green mode to Normal mode:

Step 1: Set bit UPEN to 1

Step 2: Execute a 20ms software delay

Step 3: Set bit MODE1 to 1

After Step 3, the operational mode will be changed to

the Normal mode.

· Sleep mode or Idle mode to Green mode:

Method 1: The occurrence of any reset condition

Method 2: Any active interrupt

Method 3: A Port A wake-up

Note that a Timer/Event Counter 0/1 and RTC interrupt

will not be generated when in the Idle mode as the

32768Hz crystal oscillator is stopped.

Standby Current Considerations

As the main reason for entering the Power Down Mode

is to keep the current consumption of the MCU to as low

a value as possible, perhaps only in the order of several

micro-amps, there are other considerations which must

also be taken into account by the circuit designer if the

power consumption is to be minimised. Special atten-

tion must be made to the I/O pins on the device. All

high-impedance input pins must be connected to either

a fixed high or low level as any floating input pins could

create internal oscillations and result in increased cur-

rent consumption. Care must also be taken with the

loads, which are connected to I/Os, which are setup as

outputs. These should be placed in a condition in which

minimum current is drawn or connected only to external

circuits that do not draw current, such as other CMOS

inputs. Also note that additional standby current will also

be required if the configuration options have enabled the

Watchdog Timer internal oscillator.

Wake-up

A reset, interrupt or port A wake-up can all wake up the

device from the Sleep Mode or the Idle Mode. A reset

can include a power-on reset, an external reset or a

WDT time-out reset. By examining the device status

flags, PDF and TO, the program can distinguish be-

tween the different reset conditions. Refer to the Reset

section for a more detailed description.

A port A wake-up and an interrupt can be considered as

a continuation of normal execution. Each bit in port A

can be independently selected to wake-up the device

using configuration options. When awakened by a Port

A stimulus, the program will resume execution at the

next instruction following the HALT instruction.

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