M32CSLASH8B datasheet(56/406 Pages) RENESAS

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M32C/8B Group

6. Power Supply Voltage Monitor Function

Preliminary specification

Specifications in this manual are tentative and subject to change.

REJ09B0450-0050 Rev.0.50 Oct 31, 2008

Page 39 of 385

6.1

Operation of Voltage Monitor Function

When the VDEN bit in the LVDC register is set to 1 (voltage monitor function used), the voltage monitor function

can be used after td(E-A) has elapsed.

When the voltage applied to the VCC1 pin has dropped below Vdet(F), the VMF bit in the LVDC register becomes

0 (VCC1 < Vdet(F)) and the LVDF bit in the LVDC register becomes 1 (voltage crosses Vdet). When the voltage

applied to the VCC1 pin has risen above Vdet(R), the VMF bit becomes 1 (VCC1

≥ Vdet(R)) and the LVDF bit

becomes 1.

If the LVDIEN bit in the LVDC register is 1 (voltage monitor interrupt enabled), when the value of the VMF bit is

changed, the LVDF bit becomes 1 and a voltage monitor interrupt request is generated. The LVDF bit does not

automatically become 0 when an interrupt request is acknowledged. Set it to 0 by a program. Whether the voltage

has dropped below Vdet(F) or risen above Vdet(R) can be determined by reading the VMF bit.

The voltage monitor interrupt shares the same interrupt vector with watchdog timer interrupt and oscillation stop

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

whether the voltage monitor interrupt is generated by reading the LVDF bit in the interrupt routine.

Figure 6.4 shows a voltage monitor function operation example.

Figure 6.4

Voltage Monitor Function Operation Example

Voltage applied to VCC1

Time

RESET

VDEN bit

VMF bit

LVDF bit

Voltage monitor

interrupt request

signal from LVDF bit

VDEN bit, LVDIEN bit, LVDF bit, and VMF bit: Bits in the LVDC register

NOTE:

1. Apply an "L" to the RESET pin when the voltage input to the VCC1 pin drops to 3.0 V or below. After the voltage rises above 3.0 V,

and the voltage of the main voltage regulator and the main clock oscillation stabilize, apply an "H" to the RESET pin.

Vdet(R)

3.0

(Note 1)

“H”

“L”

Vdet(F)

(V)

LVDIEN bit

td(E-A): Wait time to stablize circuit

Set to 0 by a program

“H”

“L”

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