eZ80F91 ASSP
Product Specification
39
Power-On Reset
A POR occurs every 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 continuous RESET signal to the Reset con-
troller until the supply voltage (V
CC
) exceeds the POR voltage threshold. After V
CC
rises
above V
POR
, an on-chip analog 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 shown in
V
POR
V
VBO
V
CC
= 0.0V
V
CC
= 3.3V
Program Execution
System Clock
Oscillator
Startup
Internal RESET
Signal
T
ANA
RESET mode timer delay
Figure 3. Power-On Reset Operation
Voltage Brown-Out Reset
If the supply voltage (V
CC
) drops below the V
VBO
after program execution begins, the
eZ80F91 device resets. The VBO protection circuitry detects the low supply voltage and
initiates a RESET via the Reset controller. The eZ80F91 remains in RESET until the sup-
ply voltage again returns above the POR voltage threshold (V
POR
) and the Reset controller
releases the internal RESET signal. The VBO circuitry rejects short negative brown-out
pulses to prevent spurious RESET events.
VBO operation is shown in Figure 4. The signals in the figure are not drawn to scale but
for illustration purposes only.
PS027004-0613
PRELIMINARY
Reset
ZILOG [ ZILOG, INC. ]
