mb90f352espmc1 Fujitsu Microelectronics, Inc., mb90f352espmc1 Datasheet - Page 27

• Manufacturer Part Number: mb90f352espmc1
• Description: 16-bit Proprietary Microcontrollers
• Manufacturer: Fujitsu Microelectronics, Inc.

18. Low voltage/CPU operation reset circuit
* : This value assumes the interval time at an oscillation clock frequency of 4 MHz.
19. Internal CR oscillation circuit
(1) Low voltage detection reset circuit
(2) CPU operation detection reset circuit
Oscillation frequency
Oscillation stabilization
wait time
The low voltage detection reset circuit is a function that monitors power supply voltage in order to detect when
a voltage drops below a given voltage level. When a low voltage condition is detected, an internal reset signal
is generated.
The CPU operation detection reset circuit is a 20-bit counter that uses oscillation as a count clock and generates
an internal reset signal if not cleared within a given time after startup.
When a low voltage condition is detected, the low voltage detection flag (LVRC : LVRF) is set to “1” and an
internal reset signal is output.
Because the low voltage detection reset circuit continues to operate even in stop mode, detection of a low voltage
condition generates an internal reset and releases stop mode.
During an internal RAM write cycle, low voltage reset is generated after the completion of writing. During the
output of this internal reset, the reset output from the low voltage detection reset circuit is suppressed.
The CPU operation detection reset circuit is a counter that prevents program runaway. The counter starts
automatically after a power-on reset, and must be continually and regularly cleared within a given time. If the
given time interval elapses and the counter has not been cleared, a cause such as infinite program looping is
assumed and an internal reset signal is generated. The internal reset generated from the CPU operation detection
circuit has a width of 5 machine cycles.
During recovery from standby mode, the detection period is the maximum interval plus 20 µs.
This circuit does not operate in modes where CPU operation is stopped.
The CPU operation detection reset circuit counter is cleared under any of the following conditions.
• “0” writing to CL bit of LVRC register
• Internal reset
• Main oscillation clock stop
• Transit to sleep mode
• Transit to timebase timer mode and watch mode
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Parameter
Detection voltage
/F
C
Interval time
4.0 V ± 0.3 V
(approx. 262 ms*)
Symbol
tstab
f
RC
Min
50

Value
Typ
100

MB90350E Series
Max
200
100
Unit
kHz
µs
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