MC68HC908AS32A Datasheet, PDF (42/280 Pages) Freescale Semiconductor, Inc – Microcontrollers

Memory
NOTE
Once armed, the protect option is permanently enabled. As a consequence,
all functions in the EENVR will remain in the state they were in immediately
before the security was enabled.
2.8.1.4 EEPROM Block Protection
The 512 bytes of EEPROM are divided into four 128-byte blocks. Each of these blocks can be protected
from erase/program operations by setting the EEBPx bit in the EENVR. Table 2-2 shows the address
ranges for the blocks.
Table 2-2. EEPROM Array Address Blocks
Block Number (EEBPx)
EEBP0
EEBP1
EEBP2
EEBP3
Address Range
$0800–$087F
$0880–$08FF
$0900–$097F
$0980–$09FF
These bits are effective after a reset or a upon read of the EENVR register. The block protect configuration
can be modified by erasing/programming the corresponding bits in the EENVR register and then reading
the EENVR register. See 2.8.2.2 EEPROM Array Configuration Register for more information.
NOTE
Once EEDIVSECD in the EEDIVHNVR is programmed to 0 and after a
system reset, the EEDIV security feature is permanently enabled because
the EEDIVSECD bit in the EEDIVH is always loaded with 0s thereafter.
Once this 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.
2.8.1.5 EEPROM Programming and Erasing
The unprogrammed or erase state of an EEPROM bit is a 1. The factory default for all bytes within the
EEPROM array is $FF.
The programming operation changes an EEPROM bit from 1 to 0 (programming cannot change a bit from
0 to a 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 0 to 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 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 0 to a bit that is already programmed (bit
state is already 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.
MC68HC908AS32A Data Sheet, Rev. 2.0
42
Freescale Semiconductor