4501 datasheet(159/212 Pages) RENESAS

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2.7 RAM back-up

2-42

Rev.2.01

Feb 07, 2005

4501 Group

APPLICATION

REJ09B0192-0201

2.7 RAM back-up

2.7.1 RAM back-up mode

The system enters RAM back-up mode when the POF or POF2 instruction is executed after the EPOF

instruction is executed. Table 2.7.1 shows the function and state retained at RAM back-up mode. Also,

Table 2.7.2 shows the return source from this state.

(1)

RAM back-up mode

As oscillation stops with RAM, the state of reset circuit retained, current dissipation can be reduced

without losing the contents of RAM.

Table 2.7.1 Functions and states retained at RAM back-up mode

Notes 1: “O” represents that the function can be retained, and “✕” represents that the function is initialized.

Registers and flags other than the above are undefined at RAM back-up, and set an initial value

after returning.

2: The stack pointer (SP) points the level of the stack register and is initialized to “7” at RAM back-up.

3: The state of the timer is undefined.

4: Initialize the watchdog timer flag WDF1 with the WRST instruction, and then execute the POF or

POF2 instruction.

5: The voltage drop detection circuit is operating at the RAM back-up state and sytem reset occurs

when the voltage drop is detected.

6: As for the D2/C pin, the output latch of port C is set to “1” at the RAM back-up. However, the

output latch of port D2 is retained. As for the other ports, their output levels are retained at the

RAM back-up.

Function

Program counter (PC), registers A, B, carry flag (CY), stack pointer (SP) (Note 2)

Contents of RAM

Port level

Selected oscillation circuit

Timer control register W1

Timer control registers W2, W6

Clock control register MR

Interrupt control registers V1, V2

Interrupt control register I1

Timer 1 function

Timer 2 function

A/D function

Voltage drop detection circuit

Pull-up control registers PU0–PU2

Key-on wakeup control registers K0–K2

A/D control register Q1

External 0 interrupt request flag (EXF0)

Timer 1 interrupt request flag (T1F)

Timer 2 interrupt request flag (T2F)

A/D conversion completion flag (ADF)

Watchdog timer flag (WDF1)

Watchdog timer enable flag (WEF)

16-bit timer (WDT)

Interrupt enable flag (INTE)

POF

(Note 6)

(Note 3)

O (Note 5)

(Note 3)

✕ (Note 4)

RAM back-up

POF2

(Note 6)

(Note 3)

✕ (Note 4)

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