Chapter 25 Option Byte; Functions Of Option Bytes - NEC 78K0 Series User Manual

25.1

Functions of Option Bytes

The flash memory at 0080H to 0084H of the 78K0/KE2 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
(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 (MAX.), 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.
(3) 0084H/1084H
On-chip debug operation control
• Disabling on-chip debug operation
• Enabling on-chip debug operation and erasing data of the flash memory in case authentication of the on-
chip debug security ID fails
• Enabling on-chip debug operation and not erasing data of the flash memory even in case authentication of
the on-chip debug security ID fails
Cautions 1. Be sure to set 00H (disabling on-chip debug operation) to 0084H for products not equipped
with the on-chip debug function (
78F0536, and 78F0537). Also set 00H to 1084H because 0084H and 1084H are switched at
boot swapping.
2. To use the on-chip debug function with a product equipped with the on-chip debug function
µ
( PD78F0537D), set 02H or 03H to 0084H. Set a value that is the same as that of 0084H to
1084H because 0084H and 1084H are switched at boot swapping.
Caution Be sure to set 00H to 0082H and 0083H (0082H/1082H and 0083H/1083H when the boot swap
function is used).
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CHAPTER 25 OPTION BYTE

µ
PD78F0531, 78F0532, 78F0533, 78F0534, 78F0535,
Preliminary User's Manual U17260EJ3V1UD