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HT66FM5440
Brushless DC Motor A/D Flash MCU
HT66FM5440
Brushless DC Motor A/D Flash MCU
The UART function contains a receiver RX pin wake-up function, which is enabled or disabled
by the WAKE bit in the UCR2 register. If this bit, along with the UART enable bit, UARTEN, the
receiver enable bit, RXEN and the receiver interrupt bit, RIE, are all set when the MCU enters the
power down mode with the UART clock f
H
being switched off, then a falling edge on the RX pin
will initiate an RX pin wake-up UART interrupt. Note that as it takes certain system clock cycles
after a wake-up, before normal microcontroller operation resumes, any data received during this
time on the RX pin will be ignored.
For a UART wake-up interrupt to occur, in addition to the bits for the wake-up being set, the global
interrupt enable bit, EMI, the Interrupt priority enable bit, Int_prinE, and the UART interrupt enable
bit, UARTE, must be set. If the EMI, Int_prinE and UARTE bits are not set then only a wake up
event will occur and no interrupt will be generated. Note also that as it takes certain system clock
cycles after a wake-up before normal microcontroller resumes, the UART interrupt will not be
generated until after this time has elapsed.
Low Voltage Detector – LVD
The device has a Low Voltage Detector function, also known as LVD. This enabled the device to
monitor the power supply voltage, V
DD
, and provide a warning signal should it fall below a certain
level. This function may be especially useful in battery applications where the supply voltage will
gradually reduce as the battery ages, as it allows an early warning battery low signal to be generated.
The Low Voltage Detector also has the capability of generating an interrupt signal.
LVD Register
The Low Voltage Detector function is controlled using a single register with the name LVDC. Three
bits in this register, VLVD2~VLVD0, are used to select the fixed voltage below which a low voltage
condition will be determined. A low voltage condition is indicated when the LVDO bit is set. If
the LVDO bit is low, this indicates that the V
DD
voltage is above the preset low voltage value. The
LVDEN bit is used to control the overall on/off function of the low voltage detector. Setting the bit
high will enable the low voltage detector. Clearing the bit to zero will switch off the internal low
voltage detector circuits. As the low voltage detector will consume a certain amount of power, it may
be desirable to switch off the circuit when not in use, an important consideration in power sensitive
battery powered applications.
LVDC Register
Bit
7
6
5
4
3
2
1
0
Name
—
—
LVDO
LVDEN
VBGEN
VLVD�
VLVD1
VLVD0
R/W
—
—
R
R/W
R/W
R/W
R/W
R/W
POR
—
—
0
0
0
0
0
0
Bit 7~6
Unimplemented, read as "0"
Bit 5
LVDO
: LVD Output flag
0: No Low Voltage Detected
1: Low Voltage Detected
Bit 4
LVDEN
: Low Voltage Detector Enable control
0: Disable
1: Enable