mc68hc908gp20 Freescale Semiconductor, Inc, mc68hc908gp20 Datasheet - Page 177

• Manufacturer Part Number: mc68hc908gp20
• Description: M68hc08 Family Of 8-bit Microcontroller Units Mcus
• Manufacturer: Freescale Semiconductor, Inc

11.7 FLASH Program/Margin Read Operation
MC68HC908GP20
Freescale Semiconductor
NOTE:
NOTE:
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Rev 2.1
In the other “single row case” (A6 = 0, BLK1 = 1, BLK0 = 1), the state of
A6 = 0 determines that the range from
$<A15:A12><A11:A8><A7,000><0000> to
$<A15:A12><A11:A8><A7,011><1111> is erased. Address bits
A15–A7 indicate arbitrary address bit values defined in the desired erase
address range while the remaining lower bits A6–A0 are fixed as shown.
For example, writing to address $BC87 (1011 1100 1000 0111 binary)
(A6 = 0, BLK1 = 1, BLK0 = 1) will erase the range $BC80 (1011 1100
1000 0000 binary) to $BCBF (1011 1100 1011 1111 binary).
After a total of eight program operations have been applied to a row, the
row must be erased before further programming to avoid program
disturb. An erased byte will read $00.
Programming of the FLASH memory is done on a page basis. A page
consists of eight consecutive bytes starting from address $XXX0 or
$XXX8. The purpose of the margin read mode is to ensure that data has
been programmed with sufficient margin for long-term data retention.
During margin read, the control gates of the selected memory bits are
held at a slightly negative voltage by an internal charge pump. While
performing a margin read, the operation is the same as for ordinary read
mode except that a built-in counter stretches the data access for an
additional eight cycles to allow sensing of the lower cell current. Margin
read mode imposes a more stringent read condition on the bitcell to
ensure the bitcell is programmed with enough margin for long-term data
retention. During these eight cycles the COP counter continues to run.
The user must account for these extra cycles within COP feed loops. A
margin read cycle can only follow a program operation.
To overwrite a memory location, it must first be erased to 0s then
programmed to the new value. For instance, if a location previously has
been programmed to $AA (1010 1010 binary) and the value should be
changed to $55 (0101 0101 binary), it is necessary to erase $AA to $00
FIRST before programming to $55. If the erase operation in this
example is not performed and $AA is simply re-programmed to $55, then
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