MC68HC08AS32A Datasheet, PDF (43/296 Pages) Motorola, Inc – Microcontrollers

Freescale Semiconductor, Inc.
Memory
Electrically Erasable Programmable ROM (EEPROM)
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
technique is illustrated in Table 2-3.
Table 2-3. Selective Bit Programming Description Example
Description
Original state of byte (erased)
First event is recorded by programming bit position 0
Second event is recorded by programing 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:
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.
MC68HC08AS32A — Rev. 1
MOTOROLA
Memory
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Data Sheet
43