Ram Backup State - Renesas M32R/ECU Series User Manual

17

17.2.2 RAM Backup State

Figure 17.2.3 shows the power outage RAM backup state of the M32R/ECU. When the power supply goes
down, the power supply monitor IC starts feeding current from the backup battery to the M32R/ECU. Also, the
power supply monitor IC's power outage detection pin outputs a low, causing the SBI# pin or ADnINi pin to go
low, which generates a RAM backup signal ((a) in Figure 17.2.3). Determination of whether the power is down
must be made with respect to the DC IN (regulator input) voltage in order to allow for a software processing time
at power outage.
To enable RAM backup mode, make the following setting:
(1) Create data for RAM check to verify after returning from RAM backup mode to normal mode whether the
RAM data has been retained normally ((b) in Figure 17.2.3).
If the power supply to VCC goes down after setting is made in (1), the VDDE pin voltage goes to 3.0–5.5 V and all
other pin voltages drop to 0 V, and the M32R/ECU is thereby placed in RAM backup mode ((c) in Figure 17.2.3).
DC IN
Input
Regulator
Reference voltage for
power outage detection
Backup battery
Example of RAM backup processing
(a)
Power goes down (Note 4)
Create data for
(b)
backup RAM check
(c) RAM backup mode
Figure 17.2.3 Power Outage RAM Backup State
17.2 Example of RAM Backup when Power is Down
Output
C
Power supply monitor IC
(Note 5)
VCC VDDE
(Note 1)
VREF
(Note 4)
OUT
VBB
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.
Note 4: Determined by the input level on SBI# pin or ADnINi pin.
Note 5: The time needed for processing in (2) is secured by adjusting the capacitance.
Backup power supply
for power outage
3.0–5.5V
0V
VDDE VCCE
(Note 3)
Power outage
SBI#
detection signal
(Note 2)
ADnINi
"L"
17-4
RAM BACKUP MODE
0V 0V 0V
VREFn AVCCn VCC-BUS OSC-VCC
M32R/ECU
32180 Group User's Manual (Rev.1.0)
0V