MC68HC12 MOTOROLA [Motorola, Inc], MC68HC12 Datasheet - Page 135

• Manufacturer Part Number: MC68HC12
• Description: The MC68HC912DT128A microcontroller unit (MCU) is a 16-bit device composed of standard on-chip peripherals including a 16-bit central processing unit
• Manufacturer: MOTOROLA [Motorola, Inc]

9.8 Programming EEDIVH and EEDIVL Registers
9.8.1 Normal mode
9.8.2 Special mode
MC68HC912DT128A — Rev 4.0
MOTOROLA
CAUTION:
The EEDIVH and EEDIVL registers must be correctly set according to
the oscillator frequency before any EEPROM location can be
programmed or erased.
The EEDIVH and EEDIVL registers are write once in normal mode.
Upon system reset, the application program is required to write the
correct divider value to EEDIVH and EEDIVL registers based on the
oscillator frequency. After the first write, the value in the EEDIVH and
EEDIVL registers is locked from being overwritten until the next reset.
The EEPROM is then ready for standard program/erase routines.
Runaway code can possibly corrupt the EEDIVH and EEDIVL registers
if they are not initialized (write once registers).
If an existing application code with EEPROM program/erase routines is
fixed and the system is already operating at a known oscillator
frequency, it is recommended to initialize the shadow word with the
corresponding EEDIVH and EEDIVL values in special mode. The
shadow word initializes EEDIVH and EEDIVL registers upon system
reset to ensure software compatibility with existing code. Initializing the
EEDIVH and EEDIVL registers in special modes (SMODN=0) is
accomplished by the following steps.
1. Write correct divider value to EEDIVH and EEDIVL registers
2. Remove the SHADOW word protection by clearing SHPROT bit in
3. Clear NOSHW bit in EEMCR register to make the SHADOW word
4. Write NOSHW bit in EEMCR register to make the SHADOW word
based on the oscillator frequency as per
EEPROT register.
visible at $0FC0-$0FC1.
visible at $0FC0-$0FC1.
EEPROM Memory
Programming EEDIVH and EEDIVL Registers
Table
9-1.
EEPROM Memory
Technical Data
135