UPD6P8 NEC [NEC], UPD6P8 Datasheet - Page 23

• Manufacturer Part Number: UPD6P8
• Description: MOS INTEGRATED CIRCUIT 4-BIT SINGLE-CHIP MICROCONTROLLER FOR INFRARED REMOTE CONTROL TRANSMISSION
• Manufacturer: NEC [NEC]

4.3.1 RAM retention flag (bit 3 of P3)
of the RAM are lost while the battery is being exchanged or when the battery voltage has dropped.
be judged that the RAM contents have been lost or that power has just been applied. This flag can be used to initialize
the RAM via software. After initializing the RAM and writing the necessary data to it, set this RAM retention flag
to 1 by software. At this time, 1 means that data has been set to the RAM.
The RAM retention flag indicates whether the supply voltage has fallen below the level at which the contents
This flag is at bit 3 of control register 0 (P3).
It is cleared to 0 if the supply voltage drops below the RAM retention detection voltage. If this flag is 0, it can
(1) If the supply voltage rises after the battery has been set, and exceeds V
(2) The supply voltage has now risen to the level at which the device can operate. Write the necessary data
(3) The device is reset if the supply voltage drops below V
(4) If the RAM retention flag is checked by software after reset has been cleared, it is 0. This means that
Cautions 1. The software developed for the PD67A, 68A and 69A (using the RAM retention flag) can
reset is cleared. Because the supply voltage rises from 0 V, which is lower than V
detection voltage), the RAM retention flag remains in the initial status 0.
to the RAM and set the RAM retention flag to 1.
than V
the contents of the RAM may have been lost. If this case, initialize the RAM by software.
RAM retention flag
ID
2. Unlike the PD67A, 68A and 69A, the RAM retention detection voltage of the PD6P8 is the
. Consequently, the RAM retention flag is cleared to 0.
V
be used for the PD6P8 as is.
same as the POC detection voltage. When software is newly developed, it is not necessary
to use the RAM retention flag if only the RAM is initialized by reset.
Figure 4-2. Supply Voltage Transition and Detection Voltage ( PD6P8)
POC
/V
0 V
ID
V
DD
(1)
Set to 1
Data Sheet U17848EJ3V0DS
(2)
POC
. At point (A) in the figure, the voltage is lower
(A)
(3)
Flag contents
are read
(4)
t
POC detection voltage/
RAM retention detection voltage
V
PD6P8, 6P8A, 6P8B
POC
POC
= V
(POC detection voltage),
ID
= 1.8 V (TYP.)
ID
(RAM retention
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