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Rev. 2.50
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Rev. 2.50
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HT66F20/HT66F30/HT66F40/HT66F50/HT66F60
HT66FU30/HT66FU40/HT66FU50/HT66FU60
A/D Flash MCU with EEPROM
HT66F20/HT66F30/HT66F40/HT66F50/HT66F60
HT66FU30/HT66FU40/HT66FU50/HT66FU60
A/D Flash MCU with EEPROM
• RES Pin
As the reset pin is shared with PB.0, the reset function must be selected using a configuration
option. Although the microcontroller has an internal RC reset function, if the VDD power supply
rise time is not fast enough or does not stabilise quickly at power-on, the internal reset function
may be incapable of providing proper reset operation. For this reason it is recommended that an
external RC network is connected to the RES pin, whose additional time delay will ensure that the
RES pin remains low for an extended period to allow the power supply to stabilise. During this
time delay, normal operation of the microcontroller will be inhibited. After the RES line reaches
a certain voltage value, the reset delay time t
RSTD
is invoked to provide an extra delay time after
which the microcontroller will begin normal operation. The abbreviation SST in the figures
stands for System Start-up Timer.
For most applications a resistor connected between VDD and the RES pin and a capacitor
connected between VSS and the RES pin will provide a suitable external reset circuit. Any
wiring connected to the RES pin should be kept as short as possible to minimise any stray noise
interference.
For applications that operate within an environment where more noise is present the Enhanced
Reset Circuit shown is recommended.
Note:
* It is recommended that this component is added for added ESD protection.
** It is recommended that this component is added in environments where power
line noise is significant.
Extern RES Circuit
More information regarding external reset circuits is located in Application Note HA0075E on
the Holtek website.
Pulling the RES Pin low using external hardware will also execute a device reset. In this case, as
in the case of other resets, the Program Counter will reset to zero and program execution initiated
from this point.
Note:
t
RSTD
is power-on delay, typical time=100ms
RES Reset Timing Chart