Protecting the Array | Texas Instruments TMS320F20x/F24x DSP

Reading From the Flash Array

PRELIMINARY

2.8 Reading From the Flash Array

Once the array is programmed, it is read in the same manner as other memory devices on the DSP memory interface. The flash module operates with zero wait states. When you are reading the flash module, the flash segment control register (SEG_CTR) bits should be 0 and the flash array must be in the array- access mode.

2.9 Protecting the Array

After the flash memory array is programmed, it is desirable to protect the array against corruption. The flash module of the 'F20x/F24x DSPs includes several protection mechanisms to prevent unintentional modification of the array.

Flash programming is facilitated via the supply voltage connected to the VCCP pin. If this pin is grounded, the program operation will not modify the flash array. Note, that grounding the VCCP pin does not prevent the erase operation; other protection mechanisms for the erase operation are discussed below.

The control registers provide the following mechanisms for protecting the flash array from unintentional modification.

-Segment enable bits

-EXE, KEY0, and KEY1 bits

-WDATA register

An array segment is prevented from being programmed when the correspond- ing segment enable bit in the SEG_CTR is cleared to zero. Additionally, all seg- ment enable bits are cleared by reset, making unintentional programming less likely. Even if the segment enable bits are set to one, the program, erase, and flash-write operations are not initiated unless the appropriate values are set in the EXE, KEY0, and KEY1 bits of the SEG_CTR.

At the start of an operation, the KEY1 and KEY0 bits must be written in the same write access that sets EXE. When the program pulse, erase pulse, or flash-write pulse is finished, EXE must be cleared in the same write that clears KEY1 and KEY0. The data and address latches are locked whenever the EXE bit is set, and all attempts to read from or write to the array are ignored (read data is indeterminate). Once the EXE bit is set, all register bits are latched and protected. You must clear EXE to modify the SEGx bits. This protects the array from inadvertent change. Unprotected segments cannot be masked in the same register load with the deactivation of EXE. Additional security is provided by a function of the WDATA register to prevent unintentional erasure. The WDATA register must be loaded with FFFFh before the erase operation is initi- ated. If the register is not loaded with this value, the array will not be modified.

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