MC68HC08AS32A — Rev. 1.1
Data Sheet
Freescale Semiconductor
43
security feature is armed, erase and program mode are disabled for EEDIVHNVR
and EEDIVLNVR. Modifications to the EEDIVH and EEDIVL registers are also
disabled. Therefore, be cautious on programming a value into the EEDIVHNVR.
2.5.1.5 EEPROM Programming and Erasing
The unprogrammed or erase state of an EEPROM bit is a logic 1. The factory
default for all bytes within the EEPROM array is $FF.
The programming operation changes an EEPROM bit from logic 1 to logic 0
(programming cannot change a bit from logic 0 to a logic 1). In a single
programming operation, the minimum EEPROM programming size is one bit; the
maximum is eight bits (one byte).
The erase operation changes an EEPROM bit from logic 0 to logic 1. In a single
erase operation, the minimum EEPROM erase size is one byte; the maximum is
the entire EEPROM array.
The EEPROM can be programmed such that one or multiple bits are programmed
(written to a logic 0) at a time. However, the user may never program the same bit
location more than once before erasing the entire byte. In other words, the user is
not allowed to program a logic 0 to a bit that is already programmed (bit state is
already logic 0).
For some applications it might 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 of this
NOTE:
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
program sequences (up to eight) to a unique location followed by a single erase
operation.
Table 2-3. Selective Bit Programming Description Example
Description
Program
Data
in Binary
Result
in Binary
Original state of byte (erased)
N/A
1111:1111
First event is recorded by programming bit position 0
1111:1110
Second event is recorded by programing bit position 1
1111:1101
1111:1100
Third event is recorded by programming bit position 2
1111:1011
1111:1000
Fourth event is recorded by programming bit position 3
1111:0111
1111:0000
Events five through eight are recorded in a similar fashion