IS80LV51 Datasheet, PDF (30/43 Pages) Integrated Silicon Solution, Inc – CMOS SINGLE CHIP LOW VOLTAGE 8-BIT MICROCONTROLLER

IS80LV51
IS80LV31
Power-on Reset
An automatic reset can be obtained when VCC goes
through a 10µF 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. For the IS80LV51/31, the external resistor can
be removed because the RST pin has an internal pulldown.
The capicator value can then be reduced to 1 µF (see
Figure 18).
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.
ISSI ^®
Vcc
1.0 µF ⁺
Vcc
IS80LV51/31
RST
GND
Figure 18. 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
11 OSC. PERIODS
INST
ADDR INST ADDR INST
19 OSC. PERIODS
ADDR
Figure 19. Reset Timing
30
Integrated Silicon Solution, Inc.
ADVANCE INFORMATION MC018-0A
10/01/98