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User’s Manual U17473EJ2V0UD
585
CHAPTER 26 OPTION BYTE
26.1
Functions of Option Bytes
The flash memory at 0080H to 0084H of the 78K0/LG2 is an option byte area. When power is turned on or when
the device is restarted from the reset status, the device automatically references the option bytes and sets specified
functions. When using the product, be sure to set the following functions by using the option bytes.
When the boot swap operation is used during self-programming, 0080H to 0084H are switched to 1080H to 1084H.
Therefore, set values that are the same as those of 0080H to 0084H to 1080H to 1084H in advance.
(1) 0080H/1080H
Internal low-speed oscillator operation
Can be stopped by software
Cannot be stopped
Watchdog timer interval time setting
Watchdog timer counter operation
Enabled counter operation
Disabled counter operation
Watchdog timer window open period setting
Caution
Set a value that is the same as that of 0080H to 1080H because 0080H and 1080H are
switched during the boot swap operation.
(2) 0081H/1081H
Selecting POC mode
During 2.7 V/1.59 V POC mode operation (POCMODE = 1)
The device is in the reset state upon power application and until the supply voltage reaches 2.7 V (TYP.). It
is released from the reset state when the voltage exceeds 2.7 V (TYP.). After that, POC is not detected at
2.7 V but is detected at 1.59 V (TYP.).
If the supply voltage rises to 1.8 V after power application at a pace slower than 0.5 V/ms (MIN.), use of the
2.7 V/1.59 V POC mode is recommended.
During 1.59 V POC mode operation (POCMODE = 0)
The device is in the reset state upon power application and until the supply voltage reaches 1.59 V (TYP.).
It is released from the reset state when the voltage exceeds 1.59 V (TYP.). After that, POC is detected at
1.59 V (TYP.), in the same manner as on power application.
Caution
POCMODE can only be written by using a dedicated flash programmer. It cannot be set
during self-programming or boot swap operation during self-programming (at this time, 1.59
V POC mode (default) is set).
However, because the value of 1081H is copied to 0081H
during the boot swap operation, it is recommended to set a value that is the same as that of
0081H to 1081H when the boot swap function is used.
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