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HT56R22 Datasheet(PDF) 33 Page - Holtek Semiconductor Inc

Part # HT56R22
Description  TinyPowerTM A/D Type 8-Bit OTP MCU with DAC
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Manufacturer  HOLTEK [Holtek Semiconductor Inc]
Direct Link  http://www.holtek.com
Logo HOLTEK - Holtek Semiconductor Inc

HT56R22 Datasheet(HTML) 33 Page - Holtek Semiconductor Inc

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HT56R22/HT56R23/HT56R24/HT56R25/HT56R26
Rev. 1.30
33
December 26, 2014
Mode Switching
The devices are switched between one mode and an-
other using a combination of the HLCLK bit in the
CLKMOD register and the HALT instruction. The HLCLK
bit chooses whether the system runs in either the Nor-
mal or Slow Mode by selecting the system clock to be
sourced from either a high or low frequency oscillator.
The HALT instruction forces the system into either the
Idle or Sleep Mode, depending upon whether the IDLEN
bit in CLKMOD register is set or not.
When a HALT instruction is executed and the IDLEN bit
is not set. The system enters the Sleep mode the follow-
ing conditions exist:
· The system oscillator will stop running and the appli-
cation program will stop at the
²HALT² instruction.
· The Data Memory contents and registers will maintain
their present condition.
· The WDT will be cleared and resume counting if the
WDT is enabled and clock source is selected from
fSUB. The WDT will stop if its clock source originates
from the system clock or the WDT is disabled.
· The I/O ports will maintain their present condition.
· In the status register, the Power Down flag, PDF, will
be set and the Watchdog time-out flag, TO, will be
cleared.
Power Down Mode and Wake-up
Power Down Mode
All of the Holtek microcontrollers have the ability to enter
a Power Down Mode. When the device enters this
mode, the normal operating current, will be reduced to
an extremely low standby current level. This occurs be-
cause when the device enters the Power Down Mode,
the system oscillator is 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 MCU 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.
Entering the Power Down Mode
There is only one way for the device to enter the Power
Down Mode and that is to execute the
²HALT² instruc-
tion in the application program. When this instruction is
executed, the following will occur:
· The system oscillator will stop running and the appli-
cation program will stop at the
²HALT² instruction.
· The Data Memory contents and registers will maintain
their present condition.
· The WDT will be cleared and resume counting if the
WDT clock source is selected to come from the WDT
oscillator. The WDT will stop if its clock source origi-
nates from the system clock.
· The I/O ports will maintain their present condition.
· In the status register, the Power Down flag, PDF, will
be set and the Watchdog time-out flag, TO, will be
cleared.
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 minimized. 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. This also applies to devices which
have different package types, as there may be
undonbed pins, which must either be setup as outputs
or if setup as inputs must have pull-high resistors con-
nected. Care must also be taken with the loads, which
are connected to I/O pins, 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 re-
quired if the configuration options have enabled the
Watchdog Timer internal oscillator.
Wake-up
After the system enters the Power Down Mode, it can be
woken up from one of various sources listed as follows:
· An external reset
· An external falling edge on Port A
· A system interrupt
· A WDT overflow
If the system is woken up by an external reset, the de-
vice will experience a full system reset, however, if the
device is woken up by a WDT overflow, a Watchdog
Timer reset will be initiated. Although both of these
wake-up methods will initiate a reset operation, the ac-
tual source of the wake-up can be determined by exam-
ining the TO and PDF flags. The PDF flag is cleared by a
system power-up or executing the clear Watchdog
Timer instructions and is set when executing the
²HALT²
instruction. The TO flag is set if a WDT time-out occurs,
and causes a wake-up that only resets the Program
Counter and Stack Pointer, the other flags remain in
their original status.


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