MC68HC08AZ32A Datasheet, PDF (42/312 Pages) Motorola, Inc – HCMOS Microcontroller Unit

Memory
EENVR and EEDIVNVR are nonvolatile EEPROM registers. They are programmed and erased in the
same way as EEPROM bytes. The contents of these registers are loaded into their respective volatile
registers during a MCU reset. The values in these read/write volatile registers define the EEPROM
configurations.
For EENVR, the corresponding volatile register is the EEPROM array configuration register (EEACR). For
the EEDIVNVR (two 8-bit registers: EEDIVHNVR and EEDIVLNVR), the corresponding volatile register
is the EEPROM divider register (EEDIV: EEDIVH and EEDIVL).
2.7.1.1 EEPROM Timebase Requirements
A 35µs timebase is required by the EEPROM control circuit for program and erase of EEPROM content.
This timebase is derived from dividing the CGMXCLK or bus clock (selected by EEDIVCLK bit in mask
option register B) using a timebase divider circuit controlled by the 16-bit EEPROM timebase divider
EEDIV register (EEDIVH and EEDIVL).
As the CGMXCLK or bus clock is user selected, the EEPROM timebase divider register must be
configured with the appropriate value to obtain the 35 µs. The timebase divider value is calculated by
using the following formula:
EEDIV= INT[Reference Frequency(Hz) x 35 x10^–6 +0.5]
This value is written to the EEPROM timebase divider register (EEDIVH and EEDIVL) or programmed into
the EEPROM timebase divider nonvolatile register prior to any EEPROM program or erase
operations(2.7.1 EEPROM Configuration and 2.7.1.1 EEPROM Timebase Requirements).
2.7.1.2 EEPROM Program/Erase Protection
The EEPROM has a special feature that designates the 16 bytes of addresses from $08F0 to $08FF to
be permanently secured. This program/erase protect option is enabled by programming the EEPRTCT
bit in the EEPROM nonvolatile register (EENVR) to 0.
Once the EEPRTCT bit is programmed to 0 for the first time:
• Programming and erasing of secured locations $08F0–$08FF is permanently disabled.
• Secured locations $08F0–$08FF can be read as normal.
• Programming and erasing of EENVR is permanently disabled.
• Bulk and block erase operations are disabled for the unprotected locations $0800–$08EF,
$0900–$09FF.
• Single byte program and erase operations are still available for locations $0800–$08EF and
$0900–$09FF for all bytes that are not protected by the EEPROM block protect EEBPx bits (see
2.7.1.3 EEPROM Block Protection and 2.7.3.2 EEPROM Array Configuration Register).
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.
MC68HC08AZ32A Data Sheet, Rev. 2
42
Freescale Semiconductor