MC68HC12 Datasheet, PDF (124/478 Pages) Motorola, Inc – The MC68HC912DT128A microcontroller unit (MCU) is a 16-bit device composed of standard on-chip peripherals including a 16-bit central processing unit

EEPROM Memory
9.3 EEPROM Selective Write More Zeros
The EEPROM can be programmed such that one or multiple bits are
programmed (written to a logic “0”) at a time. However, the user should
never program any bit more than once before erasing the entire byte. In
other words, the user is not allowed to over write a logic “0” with another
“0’.
For some applications it may be advantageous to track more than 10k
events with a single byte of EEPROM by programming one bit at a time.
For that purpose, a special selective bit programming technique is
available. An example is shown here.
Original state of byte = binary 1111:1111 (erased)
First event is recorded by programming bit position 0
Program write = binary 1111:1110; Result = binary 1111:1110
Second event is recorded by programming bit position 1
Program write = binary 1111:1101; Result = binary 1111:1100
Third event is recorded by programming bit position 2
Program write = binary 1111:1011; Result = binary 1111:1000
Fourth event is recorded by programming bit position 3
Program write = binary 1111:0111; Result = binary 1111:0000
Events five through eight are recorded in a similar fashion.
Note that none of the bit locations are actually programmed more than
once although the byte was programmed eight times.
When this technique is utilized, a program / erase cycle is defined as
multiple writes (up to eight) to a unique location followed by a single
erase sequence.
Technical Data
124
EEPROM Memory
MC68HC912DT128A — Rev 4.0
MOTOROLA