UPD6P8 datasheet(28/101 Pages) RENESAS

28 / 101 page

µPD6P8, 6P8A, 6P8B

Data Sheet U17848EJ5V0DS

Figure 4-4. Supply Voltage Transition and Detection Voltage (

µPD6P8A, 6P8B)

(1) If the supply voltage rises after the battery has been set, and exceeds VPOC (POC detection voltage),

reset is cleared. Because the supply voltage rises from 0 V, which is lower than VID (RAM retention

detection voltage), the RAM retention flag remains in the initial status 0.

(2) The supply voltage has now risen to the level at which the device can operate. Write the necessary data

to the RAM and set the RAM retention flag to 1.

(3) The device is reset if the supply voltage drops below VPOC. At point (A) in the above figure, the RAM

retention flag remains 1 because the supply voltage is higher than VID at this point.

(4) If the RAM retention flag is checked by software after reset has been cleared, it is 1. This means that

the contents of the RAM have not been lost. It is therefore not necessary to initialize the RAM by software.

(5) The device is reset if the supply voltage drops below VPOC. At point (B) in the figure, the voltage is lower

than VID. Consequently, the RAM retention flag is cleared to 0.

(6) If the RAM retention flag is checked by software after reset has been cleared, it is 0. This means that

the contents of the RAM may have been lost. If this case, initialize the RAM by software.

VDD

VPOC

VID

0 V

RAM retention flag

(A)

(B)

(6)

(5)

(4)

(3)

(2)

Set to 1

Flag contents

are read

Flag contents

are read

(1)

POC detection voltage

(Refer to 8. POC CIRCUIT)

VPOC = 1.8 V (TYP.)

RAM retention detection voltage

VID = 1.6 V (TYP.)

UPD6P8 Datasheet(PDF) 28 Page - Renesas Technology Corp