AN2156 Freescale Semiconductor / Motorola, AN2156 Datasheet - Page 23

• Manufacturer Part Number: AN2156
• Description: Programming and Erasing FLASH and EEPROM Memories on the MC68HC908AS60A/AZ60A
• Manufacturer: Freescale Semiconductor / Motorola

AN2156
MOTOROLA
NOTE:
NOTE:
NOTE:
The EExDIVHNVR and EExDIVLNVR registers consist of nonvolatile
memory. Therefore, programming or erasing these locations requires
the normal EEPROM program/erase sequences, which are described in
later sections. On the other hand, the EExDIVH and EExDIVL do not
consist of nonvolatile memory. Whenever reset occurs, values in the
EExDIVHNVR and EExDIVLNVR are automatically loaded into the
EExDIVH and EExDIVL, respectively. These registers are also writable
in software.
EEDIVSECD — EEPROM Divider Security Disable Bit
This security feature is enabled when EEDIVSECD in the EExDIVHNVR
is programmed to 0 and then the system is reset.
EEDIV10–EEDIV0 — EEPROM Timebase Prescaler Bits
The EExDIVH and EExDIVL registers are writable anytime that EELAT
is cleared and EEDIVSECD is set. However, modified values are held
only until the next reset.
The EExDIV value is calculated by using this formula:
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This bit enables/disables the security feature of the EExDIV registers.
When the EExDIV security feature is enabled (EEDIVSECD is
programmed to logic 0 in the EExDIVHNVR), the registers EExDIVH,
EExDIVL, EExDIVHNVR, and EExDIVHNVR are locked permanently.
These prescaler bits store the value of EExDIV which is used as the
divisor to derive a timebase of 35 s from the selected reference clock
source (CGMXCLK or bus clock) for the EEPROM related internal
timer and circuits. EEDIV10–EEDIV0 are readable at any time.
Freescale Semiconductor, Inc.
EExDIV = INT [Reference Frequency (Hz) x (35 x 10
For More Information On This Product,
1 = EExDIV security feature disabled
0 = EExDIV security feature enabled
$FE1B, EEPROM-1 divider low register, EE1DIVL
$FF70, EEPROM-2 nonvolatile register, EE2DIVHNVR
$FF71, EEPROM-2 nonvolatile register, EE2DIVLNVR
$FF7A, EEPROM-2 divider high register, EE2DIVH
$FF7B, EEPROM-2 divider low register, EE2DIVL
Configuration Register 2 and EEPROM Timebase Divider Control Registers
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-6
) + 0.5 ]
Application Note
23