
Rev. 1.40
54
March 29, 2019
Rev. 1.40
55
March 29, 2019
HT45F23A/HT45F24A
TinyPower
TM
Flash MCU with OPA & Comparators
HT45F23A/HT45F24A
TinyPower
TM
Flash MCU with OPA & Comparators
RES
Pin
As the reset pin is shared with PB.6, 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
.
External 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 devices 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.
RES
Reset Timing Chart