Holtek HT67F2350 Manual page 99

HT67F2350/HT67F2360
HT67F2370/HT67F2390
Advanced A/D Flash MCU with LCD & EEPROM
RES Pin Reset
As the reset pin is shared with I/O pins, the reset function must be selected using a control register,
RSTC. 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
microcontroller will begin normal operation. The abbreviation SST in the figures stands for System
Start-up Time. For most applications a resistor connected between VDD and the RES line and a
capacitor connected betweeb 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.
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.
Rev. 1.60
, is invoked to provide an extea delay time after which the
RSTD
V
DD
0.01µF**
1N4148*
10kΩ~
100kΩ
300Ω*
0.1µF~1µF
External RES Circuit
0.4V
RES DD
Internal Reset
Note: t is power-on delay with typical time=16 ms
RSTD
RES Reset Timing Chart
99
VDD
RES
VSS
0.9V
DD
t +t
RSTD SST
May 16, 2019