AN2183 Freescale Semiconductor / Motorola, AN2183 Datasheet - Page 2

• Manufacturer Part Number: AN2183
• Description: Using FLASH as EEPROM on the MC68HC908GP32
• Manufacturer: Freescale Semiconductor / Motorola

Application Note
FlashEE Implementation
2
In order to verify the correct operation of the FlashEE routines, a test
program is included in this application note. This program demonstrates
how these routines would be integrated into a project. The test program
communicates with a host computer via a simple RS-232 connection in
order to facilitate testing. User programs that include the FlashEE
routines are free to implement them as one would commonly expect to
use EEPROM algorithms for various forms of data storage.
Specifications for the M68HC908 Family FLASH memory indicate a
program/erase cycle endurance of 10,000 cycles across the full
operating temperature range. This is typically more than sufficient for
most applications. However, this value can be mathematically elongated
by the number of times a small data block can fit within a FLASH erase
page.
It is important to note that the while the FLASH memory is “page”
erasable, it is, in fact, byte programmable. It’s organization is configured
for efficient “row” programming, but any algorithm must write each
location on a byte-by-byte basis. There is no limit to the minimum
number of bytes that must be programmed within a row. But every time
a row is programmed, the high voltage charge pump must be enabled
and disabled, regardless of the number of bytes that are programmed.
A critical FLASH memory specification is the cumulative program high
voltage period. This is the maximum total time that a specific FLASH
program row is subjected to being programmed between erasures. The
technical data for the MC68HC908GP32 lists this maximum
specification as being 4 ms.
The subroutines herein are optimized to program relatively small blocks
of data sequentially within the FLASH memory, thereby minimizing the
total cumulative length of time spent programming. These subroutines
will only erase the FlashEE space when there is no more room for the
next data block. Each FLASH erase page consists of two program rows.
The FLASH erase page size for the MC68HC908GP32 is 128 bytes.
Freescale Semiconductor, Inc.
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MOTOROLA
AN2183