17
17-5
RAM BACKUP MODE
32180 Group User's Manual (Rev.1.0)
RAM backup signal
External circuit
Port X
(Note 1)
IB
VREFn
SBI#
ADnINi
M32R/ECU
(Note 3)
RAM backup power supply
Regulator
VDDE
DC IN
Input Output
Regulator
AVCCn
(Note 2)
VCCE
Output
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.
OSC-VCC
VCC-BUS
Figure 17.3.1 Typical RAM Backup Circuit for Saving Power Consumption
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.
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.
Figure 17.3.2 Normal Operating State (when VCCE = 5 V)
RAM backup signal
(Note 1)
External circuit
Port X
IB
VREFn
SBI#
ADnINi
M32R/ECU
(Note 3)
RAM backup power supply
Regulator
VDDE
DC IN
Input Output
Regulator
AVCCn
(Note 2)
VCCE
Output
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.
VCC-BUS
OSC-VCC
"H"
"H"
"H"
5V 5V 5V 5V 5V 5V
17.3 Example of RAM Backup for Saving Power Consumption
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