upd17240 Renesas Electronics Corporation., upd17240 Datasheet - Page 60

• Manufacturer Part Number: upd17240
• Description: 4-bit Single-chip Microcontrollers For Small General-purpose Infrared Remote Control Transmitters
• Manufacturer: Renesas Electronics Corporation.

7.
7.1
below the level at which the contents of the RAM are lost while the battery is being exchanged or when the battery
voltage has dropped.
this flag is 0, it can 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.
60
The RAM retention flag (bit 0 of the register file at address 21H) indicates whether the supply voltage has dropped
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 (approx. 1.4 V TYP.). If
(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 to
(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 1. This means that the
(5) The device is reset if the supply voltage drops below V
(6) If the RAM retention flag is checked by software after reset has been cleared, it is 0. This means that the
RAM RETENTION DETECTOR
RAM Retention Flag
RAM retention flag
is cleared. Because the supply voltage rises from 0 V, which is lower than V
voltage), the RAM retention flag remains in the initial status 0.
the RAM and set the RAM retention flag to 1.
flag remains 1 because the supply voltage is higher than V
contents of the RAM have not been lost. It is therefore not necessary to initialize the RAM by software.
V
contents of the RAM may have been lost. If this happens, initialize the RAM by software.
ID
. Consequently, the RAM retention flag is cleared to 0.
V
0 V
POC
V
ID
V
DD
Figure 7-1. Supply Voltage Transition and Detection Voltage
(1)
µ PD17240, 17241, 17242, 17243, 17244, 17245, 17246
Set to 1
(2)
Flag content is read.
Data Sheet U15002EJ1V1DS
(A)
(3)
(4)
POC
POC
(B)
(5)
. At point (A) in the above figure, the RAM retention
. At point (B) in the figure, the voltage is lower than
ID
Flag content is read.
at this point.
(6)
t
POC detection voltage
V
RAM retention detection voltage
V
POC
POC
ID
= 1.4 V (TYP.)
= 1.85 V (TYP.)
(POC detection voltage), reset
ID
(RAM retention detection