EZ80F91MCU Datasheet, PDF (71/396 Pages) Zilog, Inc. – eZ80Acclaim-TM Flash Microcontrollers

eZ80F91 MCU
Product Specification
52
Power-On Reset
A Power-On Reset (POR) occurs each time the supply voltage to the part rises
from below the voltage brown-out threshold (V_VBO) to above the POR voltage
threshold (V_POR). The internal bandgap-referenced voltage detector sends a con-
tinuous RESET signal to the Reset controller until the supply voltage (V_CC)
exceeds the POR voltage threshold. After V_CC rises above V_POR, an on-chip ana-
log delay element briefly maintains the RESET signal to the Reset controller. After
this analog delay element times out, the Reset controller holds the eZ80F91 in
RESET until the RESET mode timer expires. POR operation is illustrated in
Figure 3. The signals in Figure 3 are not drawn to scale, but are for illustration pur-
poses only.
V_POR
V_VBO
V_CC = 0.0V
V_CC = 3.3V
Program Execution
System Clock
Internal RESET
Signal
Oscillator
Startup
T_ANA
Figure 3. Power-On Reset Operation
RESET mode timer delay
Voltage Brown-Out Reset
If, after program execution begins, the supply voltage (V_CC) drops below the volt-
age brown-out threshold (V_VBO), the eZ80F91 device resets. The VBO protection
circuitry detects the low supply voltage and initiates a RESET via the Reset con-
troller. The eZ80F91 remains in RESET until the supply voltage again returns
above the POR voltage threshold (V_POR) and the Reset controller releases the
internal RESET signal. The VBO circuitry rejects very short negative brown-out
pulses to prevent spurious RESET events.
PS019209-0504
PRELIMINARY
Reset