MC908AS60ACFU Datasheet, PDF (75/414 Pages) Freescale Semiconductor, Inc – M68HC08 Microcontrollers

Functional Description
6.4.5 EEPROM-1 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-1 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-1 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 technique is illustrated in Table 6-2.
Table 6-2. Example Selective Bit Programming Description
Description
Original state of byte (erased)
First event is recorded by programming bit position 0
Second event is recorded by programming bit position 1
Third event is recorded by programming bit position 2
Fourth event is recorded by programming bit position 3
Events five through eight are recorded in a similar fashion
Program Data
in Binary
n/a
1111:1110
1111:1101
1111:1011
1111:0111
Result
in Binary
1111:1111
1111:1110
1111:1100
1111:1000
1111:0000
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 program sequences (up to
eight) to a unique location followed by a single erase operation.
6.4.5.1 Program/Erase Using AUTO Bit
An additional feature available for EEPROM-1 program and erase operations is the AUTO mode. When
enabled, AUTO mode will activate an internal timer that will automatically terminate the program/erase
cycle and clear the EEPGM bit. Please see 6.4.5.2 EEPROM-1 Programming, 6.4.5.3 EEPROM-1
Erasing, and 6.5.1 EEPROM-1 Control Register for more information.
MC68HC908AZ60A • MC68HC908AS60A • MC68HC908AS60E Data Sheet, Rev. 6
Freescale Semiconductor
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