BS83B08-3 Datasheet, PDF (48/141 Pages) Holtek Semiconductor Inc – 8-Bit Touch Key Flash MCU

BS83B08-3/B12-3/B16-3/B16G-3/C24-3
8-Bit Touch Key Flash MCU
RES Pin
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.
V DD
0 .0 1 m F * *
VDD
1N 4148*
10kW ~
100kW
0 .1 ~ 1 m F
RES
300W *
VSS
Note:
²*² It is recommended that this component is added for added ESD protection
²**² 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 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.
RES
0 .4 V D D
0 .9 V D D
tR S T D + tS S T
In te rn a l R e s e t
Note: t_RSTD is power-on delay, typical time=50ms for BS83C24-3, =100ms except BS83C24-3.
RES Reset Timing Chart
The RES bit in the CTRL register indicates what kind of reset has occurred. This bit can only be set
high by the external reset pin. Any other software reset type will clear the bit to zero. If the application
reads this bit and it is high then this indicates that a hardware reset has occurred. After reading the bit it
should be cleared to zero by the application program. Note however that after a power-on reset this pin
will be in an unknown condition.
Rev. 1.30
48
September 22, 2011