Configuration Of Low Voltage And Cpu Operation Detection Reset Circuit; Fig. 24.1 Block Diagram Of Detection Reset Circuit For Low Voltage And Cpu Operation - Fujitsu MB90420/5 (A) Series Hardware Manual

MB90420/5 (A) SERIES F

24.2 Configuration of Low Voltage and CPU Operation Detection Reset Circuit

The detection reset circuit for low voltage and CPU operation consists of the following 3 blocks:
• CPU operation detection circuit
• Voltage compare circuit
• Detection reset control register for low voltage and CPU operation (LVRC)
n Block diagram for detection reset circuit for low voltage and CPU operation
CPU operation detector
Oscillation
clock
Counter

Fig. 24.1 Block Diagram of Detection Reset Circuit for Low Voltage and CPU Operation

• CPU operation detection circuit
This circuit prevents program runaway. After being started, this circuit must be cleared at regular intervals.
• Voltage compare circuit
H is output when a low voltage is detected by comparing the detection voltage value and power supply
voltage.
The voltage comparator operates constantly after power-on.
• Detection reset control register for low voltage and CPU operation (LVRC)
The detection reset flag for low voltage and CPU operation is cleared and the CPU operation detection
function counter is cleared.
• Reset factor for detection reset circuit for low voltage and CPU operation
When the power supply voltage is below than the detection voltage value, an internal reset occurs.
An internal reset occurs when the counter of the CPU operation detector is not cleared within a fixed period
of time after being started.
2
MC-16LX FAMILY 16-BIT MICROCONTROLLERS HARDWARE MANUAL
F/F
OF
Clear
RESV0 RESV0 RESV1
Internal data bus
V
Voltage
comparator
–
+
Fixed voltage source
Noise canceller
RESV1 CL LVRF RESV0
Low-voltage detection reset control register (LVRC)
24-4
CC
V
SS
Internal reset
Internal reset
CPUF