參數(shù)資料
型號： UPD17246MC-xxx-5A4
廠商： NEC Corp.
英文描述： 4-BIT SINGLE-CHIP MICROCONTROLLERS FOR SMALL GENERAL-PURPOSE INFRARED REMOTE CONTROL TRANSMITTERS
中文描述： 4位單片微控制器的小型通用兩用紅外遙控遞質(zhì)
文件頁數(shù)： 60/102頁
文件大?。?/td> 461K
代理商： UPD17246MC-XXX-5A4
60
Data Sheet U15002EJ1V0DS
μ
PD17240, 17241, 17242, 17243, 17244, 17245, 17246
7.
RAM RETENTION DETECTOR
7.1
RAM Retention Flag
The RAM retention flag (bit 0 of the register file at address 21H) indicates whether the supply voltage has dropped
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 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
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.
Figure 7-1. Supply Voltage Transition and Detection Voltage
V
DD
V
POC
V
ID
0 V
RAM retention flag
(A)
(B)
(6)
(5)
(4)
(3)
(2)
Set to 1
Flag content is read.
Flag content is read.
(1)
t
POC detection voltage
V
POC
= 1.85 V (TYP.)
RAM retention detection voltage
V
ID
= 1.4 V (TYP.)
(1) If the supply voltage rises after the battery has been set, and exceeds V
POC
(POC detection voltage), reset
is cleared. Because the supply voltage rises from 0 V, which is lower than V
ID
(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 V
POC
. At point (A) in the above figure, the RAM retention
flag remains 1 because the supply voltage is higher than V
ID
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 V
POC
. At point (B) in the figure, the voltage is lower than
V
ID
. 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 happens, initialize the RAM by software.
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