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M32C/8A Group

6. Power Supply Voltage Detection Function

Rev.1.00

Jul 15, 2007

Page 42 of 352

REJ09B0385-0100

6.2

Vdet4 Detection Function

Vdet4 detection interrupt is generated if the voltage applied to the VCC1 pin crosses the Vdet4 (V) level, either by

dropping below or by rising above Vdet4. Set the VC27 bit in the VCR2 register to 1 (Vdet4 detection function

used) and the D40 bit in the D4INT register to 1 (Vdet4 detection interrupt enabled) to use the Vdet4 detection

function.

The D42 bit becomes 1 (voltage crosses Vdet4) as soon as the applied voltage crosses Vdet4. When the D42 bit

changes from 0 to 1, a Vdet4 detection interrupt request is generated. The D42 bit does not become 0 automatically

when the interrupt is acknowledged. Set it to 0 (not detected) by program. Whether the voltage has dropped below

Vdet4 or risen above Vdet4 can be determined by reading the VC13 bit in the VCR1 register.

Set the D41 bit in the D4INT register to 1 to use the Vdet4 detection interrupt to exit wait mode or stop mode. The

MCU exits wait mode or stop mode if the Vdet4 detection signal is generated even if the D42 bit is 1.

The Vdet4 detection interrupt shares the same interrupt vector with watchdog timer interrupt and oscillation stop

detection interrupt. When using the Vdet4 detection interrupt simultaneously with these interrupts, determine

whether the Vdet4 detection interrupt is generated by reading the D42 bit in the interrupt routine.

Table 6.1 shows conditions to generate Vdet4 detection interrupt request. Figure 6.6 shows a Vdet4 detection

function operation example.

Bits DF1 and DF0 in the D4INT register determine the sampling clock which is used to detects if the voltage

applied to the VCC1 pin crosses Vdet4. Table 6.2 shows the sampling periods.

− : either 0 or 1

NOTES:

1. Set to 0 by program before generating an interrupt.

2. An interrupt request is generated when the sampling period elapses after the value of the bit is changed. See

Figure 6.6 Vdet4 Detection Function Operation Example

for details.

3. CPU operating mode includes main clock mode, PLL mode, low speed mode, low-power consumption mode,

on-chip oscillator mode, on-chip oscillator low-power consumption mode. (Refer to 9. Clock Generation

Circuits

4. Refer to 6.2.1 Usage Notes on Vdet4 Detection Interrupt.

NOTE:

1. Set the CPU clock below 24 MHz to use the voltage detection function.

Table 6.1

Conditions to Generate Vdet4 Detection Interrupt Request

Operating Mode

VC27 Bit

D40 Bit

D41 Bit

D42 Bit(1)

VC13 Bit(2)

CPU operating mode(3)

−

0 to 1

1 to 0

Wait mode, Stop mode(4)

−

0 to 1

Table 6.2

Sampling Periods

CPU Clock

(MHz)

Sampling Clock (

μs)

Divided-by-8

Divided-by-16

Divided-by-32

Divided-by-64

3.0

6.0

12.0

24.0

2.0

4.0

8.0

16.0

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