Texas Instruments TMS320F20x/F24x DSP manual Preliminary

Operations that Modify the Contents of the 'F20x/F24x Flash Array

PRELIMINARY

2.1 Operations that Modify the Contents of the 'F20x/F24x Flash Array

Operations that modify the contents of the flash array are generically referred to as either ªprogramming,º which drives one or more bits toward the logic zero state, or ªerasing,º which drives all bits towards the logic one state. It should be noted that since these operations are performed incrementally, a single ªprogrammingº or ªerasingº operation does not ALWAYS result in a valid logic one or zero. The result of each of these types of operations depends on the initial state of the bit(s) prior to the operation. This is described in more detail below.

Within these two basic types of operations (which are related to the fact that there are only two valid logic levels in the F20x/F24x device) are four distinctly different types of functions which are actually performed.

In the category of ªprogrammingº operations, there are three actual types of functions that are performed:

-Clear ± which is used to write ALL array bits to a zero state,

-Program ± which is used to write SELECTED array bits to zero, and

-Flash-Write ± which is used to recover ALL array bits from depletion In the category of ªeraseº operations, there is only one type of operation:

-Erase ± which is used to write ALL array bits to a one state.

Clear, Program, Flash-Write, and Erase are the only four functions that are used to modify the flash array.

Assuming that the intent of a modification of the contents of the flash array is to program the array with a selection of ones and zeroes, the following se- quence of operations must be performed for proper operation of the flash memory:

1)The array is first CLEARED to all zeroes.

2)The array is then ERASED to all ones.

3)The array is then checked for depletion and recovered using FLASH- WRITE if necessary (note that if Flash-Write is used to recover from deple- tion, this sequence must be started over again with the Clear and Erase functions).

4)Once the array is properly cleared and erased, and verified not to be in depletion, the array is then PROGRAMMED with the desired selection of zero bits.

2-2 PRELIMINARY