Mitsubishi Electric M32R Series User Manual page 748

Mitsubishi 32-bit risc single-chip microcomputers

Table of Contents

17.1 Outline

In RAM backup mode, the contents of the internal RAM are retained while the power is turned off.

RAM backup mode is used for the following two purposes:

• Back up the internal RAM data when the power is down

• Turn off the power to the CPU whenever necessary to save on the system's power

The 32R/E CPU is placed in RAM backup mode by applying a voltage of 2.0-3.3 V to the VDD pin

(provided for RAM backup) and 0 V to all other pins. During RAM backup mode, the contents of the

internal RAM are retained, while the CPU and internal peripheral I/O remain idle. Also, because all

pins except VDD are held low during RAM backup mode, power consumption in the system can

effectively reduced.

17.2 Example of RAM Backup when Power is Down

A typical circuit for RAM backup at power outage is shown in Figure 17.2.1. The following explains

how the RAM can be backed up by using this circuit as an example.

(3.3V system)

Reference voltage for

power outage detection

Backup battery

Note 1 : Power outage is detected by the DC IN (regulator input) voltage.

Note 2 : These pins are used to detect a RAM backup signal.

Note 3 : This pin outputs a high when the power is on and outputs a low when the power is down.

Figure 17.2.1 Typical Circuit for RAM Backup at Power Outage

Power supply

Backup power supply

for power outage

Power outage

detection signal

RAM BACKUP MODE

17.1 Outline