Example Of Ram Backup For Saving Power Consumption; Normal Operating State - Renesas M32R/ECU Series User Manual

17

17.3 Example of RAM Backup for Saving Power Consumption

A typical RAM backup circuit for saving the microcomputer's power consumption is shown in Figure 17.3.1. The follow-
ing explains how the RAM is backed up for the purpose of low-power operation by using this circuit as an example.
DC IN
External circuit
RAM backup signal
(Note 1)
Note 1: This circuit outputs a low during RAM backup.
Note 2: This port outputs a high when the power is on, and is set for input mode when in RAM backup mode.
Note 3: These pins are used to detect a RAM backup signal.
Figure 17.3.1 Typical RAM Backup Circuit for Saving Power Consumption

17.3.1 Normal Operating State

Figure 17.3.2 shows the normal operating state of the M32R/ECU. During normal operation, the RAM backup
signal output by the external circuit is high. Also, input on the SBI# pin or ADnINi (i = 0–15) pin which is used to
detect a RAM backup signal remains high.
Port X, which connects to the transistor's base, should output a high. This causes the transistor's base voltage,
IB, to go high, so that current is fed from the power supply to the VCCE pin via the transistor.
DC IN
External circuit
RAM backup signal
(Note 1)
Note 1: This circuit outputs a low during RAM backup.
Note 2: This port outputs a high when the power is on, and is set for input mode when in RAM backup mode (one of the port pins selected).
Note 3: These pins are used to detect a RAM backup signal.
Figure 17.3.2 Normal Operating State (when VCCE = 5 V)
17.3 Example of RAM Backup for Saving Power Consumption
Input
IB
SBI#
ADnINi
Input
IB
"H"
"H"
SBI#
ADnINi
Output
RAM backup power supply
Regulator
Output
Regulator
OSC-VCC
VCCE
Port X
(Note 2)
(Note 3)
M32R/ECU
Output
RAM backup power supply
Regulator
Output
Regulator
5V 5V
"H"
VCC-BUS
VCCE
Port X
(Note 2)
(Note 3)
M32R/ECU
17-5
RAM BACKUP MODE
VREFn VCC-BUS AVCCn VDDE
5V 5V 5V 5V
VREFn OSC-VCC AVCCn VDDE
32180 Group User's Manual (Rev.1.0)