IC80C54 Datasheet, PDF (8/22 Pages) Integrated Circuit Solution Inc – CMOS SINGLE CHIP 8-BIT MICROCONTROLLER

IC80C54
IC80C58
Power-on Reset
An automatic reset can be obtained when VCC goes through
a 10 µF capacitor and GND through an 8.2K resistor,
providing the Vcc rise time does not exceed 1 msec and the
oscillator start-up time does not exceed 10 msec. This
Power-on reset circuit is shown if Figure 21. The CMOS
devices do not require the 8.2K pulldown resistor, although
its presence does no harm.
When power is turned on, the circuit holds the RST pin high
for an amount of time that depends on the value of the
capacitor and the rate at which it charges. To ensure a good
reset, the RST pin must be high long enough to allow the
oscillator time to start-up (normally a few msec) plus two
machine cycles.
Note that the port pins will be in a random state until the
oscillator has start and the internal reset algorithm has
written 1s to them.
With this circuit, reducing VCC quickly to 0 causes the RST
pin voltage to momentarily fall below 0V. However, this
voltage is internally limited and will not harm the device.
Vcc
+
10 F
-
8.2K Ω
Vcc
IC80C54/58
RST
GND
Figure 6. Power-On Reset Circuit
12 OSC. PERIODS
S5 S6 S1 S2 S3 S4 S5 S6 S1 S2 S3 S4 S5 S6 S1 S2 S3 S4
RST
SAMPLE
RST
SAMPLE
RST
INTERNAL RESET SIGNAL
ALE
PSEN
P0
INST ADDR INST ADDR INST ADDR INST ADDR INST ADDR
11 OSC. PERIODS
19 OSC. PERIODS
Figure 7. Reset Timing
8
Integrated Circuit Solution Inc.
MC003-0B