Introduction:
Some enhanced mid-range Microchip PIC devices support High-Endurance Flash (HEF) memory. These devices lack the data EEPROM
found on other devices.
Instead, they implement an equivalent amount of special flash memory, called HEF memory, that can provide an endurance comparable
to that of a traditional data EEPROM.
HEF memory can be erased and written 100,000 times.
HEF memory appears in the regular program memory space and can be used for any purpose, like regular flash program memory.
As with all flash memory, data must be erased before it can be written and writing this memory will stall the device.
Methods to read, write and erase the HEF memory are included in GCBASIC and they are described in this introduction. Also
see Microchip application note AN1673, Using the PIC16F1XXX High-Endurance Flash (HEF) Block.
The hefsaf.h library supports HEF operations for GCBASIC.
Note: By default, GCBASIC will use HEF memory for regular executable code unless it is told otherwise.
If you wish to store data here, you should reserve the HEF memory by using the compiler option, as shown below to reserve
128 words of HEF memory:
#option ReserveHighProg 128
HEF memory is a block of memory locations found at the top of the flash program memory.
Each memory location can be used to hold a 8-bit byte value.
To further explain, the PIC 16F Enhanced Midrange Sevices memory architecture is 14-bits wide. Therefore, for a single
14-bit memory location it is only practical to store an 8-bit byte value, and two 14-bit memory locations to hold one 16-bit
word value.
This is because the memory architecture only allows the use of the the lower 8-bits of each 14-bit flash memory location
for HEF usage
The main difference between HEF memory and EEPROM is that EEPROM allows byte-by-byte erase whereas the HEF memory does not.
With HEF memory, data must be erased before a write and the erase can only be performed in blocks of memory.
The blocks, also called rows, are a fixed size associated with the specific device.
GCBASIC handles the erase operation automatically.
When a write operation is used by a user the GCBASIC library reads to a cache, updates the cache, erase the block and finally
write the caches.
The complexity of using HEF memory is reduced with the automatically handling of these operations.
The hefsaf.h library provides a set of methods to support the use of HEF memory.
|
Method |
Parameters |
Usage |
|
|
a subroutine with the parameters: location, byte value |
HEFWrite ( location, byte_variable ) |
|
|
a subroutine with the parameters: location, word_value |
HEFWriteWord ( location, word_variable ) |
|
|
a function with the parameters: location returns a byte value |
byte_variable = HEFRead ( location ) |
|
|
a subroutine with the paramers: location, byte_value |
HEFRead ( location , out_byte_variable ) |
|
|
a function with the parameters: location returns a word value |
word_variable = HEFRead ( location ) |
|
|
a subroutine with the parameters: location, word_value |
HEFRead ( location , out_word_variable ) |
|
|
a subroutine with the parameters: block_number |
HEFEraseBlock ( 0 )
|
|
|
a subroutine with the parameters: block_number, buffer() [, HEF_ROWSIZE_BYTES ] |
HEFWriteBlock( 0, myMemoryBuffer ) 'where myMemoryBuffer is an Array or a String
|
|
|
a subroutine with the parameters: block_number, buffer() [, HEF_ROWSIZE_BYTES ] |
HEFReadBlock( 0, myMemoryBuffer ) 'where myMemoryBuffer is an Array or a String.
|
The library also defines a set constants that are specific to the device.
These may be useful in the user program.
These constants are used by the library.
A user may use these public constants.
|
Constant |
Type |
Usage |
|
|
Byte |
Size of an HEFM block in words |
|
|
Word or a Byte |
ChipHEFMemWords parameter from the device .dat file |
|
|
Word |
Starting address of HEFM |
|
|
Byte |
Number of blocks of HEFM |
|
|
Word |
Device specific constant for the total flash size |
|
|
Word |
Device specific constant for the number of HEFM words available |
|
|
Word |
Device specific constant for the number of HEFM in an erase row |
Warning
Whenever you update the hex file of your Microchip PIC micro-controller with your programmer you MAY erase the data that are
stored in HEF memory.
If you want to avoid that you will have to flash your Microchip PIC micro-controller with software that allows memory exclusion
when flashing.
This is the case with Microchip PIC MPLAB IPE (Go to Advanced Mode/Enter password/Select Memory/Tick “Preserve Flash on Program”/
Enter Start and End address of your HEFM). Or, simply use the PICkitPlus suite of software to preserve HEF memory during programming.
See also
HEFRead,
HEFReadWord,
HEFWrite,
HEFWriteWord,
HEFReadBlock,
HEFWriteBlock,
HEFEraseBlock
