EEPROM-1 Memory
Functional Description
MC68HC908AZ60A — Rev 2.0 Technical Data
MOTOROLA EEPROM-1 Memory 95
6.5.5 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.
Note that none of the bit locations are actually programmed more than
once although the byte was programmed eight times.
Table 6-2. Example Selective Bit Programming Description
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 1111:1110
Second event is recorded by programming 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
