MC68HC08AS20 Datasheet, PDF (63/386 Pages) Freescale Semiconductor, Inc – M68HC08 Microcontrollers

erase. Any attempts to read other EEPROM data will read the
latched data. If EELAT is set, other writes to the EECR will be
allowed after a valid EEPROM write.
b. To ensure proper erasing sequence, the EEPGM bit cannot
be set if the EELAT bit is cleared and a non-EEPROM write
has occurred. Once EEPGM is set, the type of erase mode
cannot be modified. If EEPGM is set, the on-board charge
pump generates the erase voltage and applies it to the user
EEPROM array. When the EEPGM bit is cleared, the erase
voltage is removed from the array and the internal charge
pump is turned off.
c. Any attempt to clear both EEPGM and EELAT bits with a
single instruction will clear only EEPGM to allow time for
removal of high voltage from the EEPROM array.
In general, all bits should be erased before being programmed.
However, if program/erase cycling is of concern, the following procedure
can be used to minimize bit cycling in each EEPROM byte. If any bit in
a byte must be changed from a 0 to a 1, the byte needs to be erased
before programming. Table 6-1 summarizes the conditions for erasing
before programming.
Table 6-1. EEPROM Program/Erase Cycling Reduction
EEPROM Data To Be
Programmed
0
0
1
1
EEPROM Data Before
Programming
0
1
0
1
Erase Before
Programming?
No
No
Yes
No
MC68HC08AS20 — Rev. 4.1
Freescale Semiconductor
Advance Information
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