PRELIMINARY
Programming (or Clear) Algorithm
Another important consideration is the total amount of time required to do the programming. The number of programming pulses required to completely pro- gram a flash memory cell increases as ambient temperature increases and/or supply voltage decreases. More programming pulses are required when the minimum supply voltage is used than when the nominal or maximum supply voltage is used. The number of program pulses required also increases throughout the life of the device, as more
The algorithm incorporates the steps for applying a program pulse (outlined in Table 3±1) along with some other techniques to ensure margin. In general, not all flash bits require the same number of program pulses to reach the pro- grammed margin level. For this reason, the programming algorithm applies a series of short program pulses until the memory location is programmed. How- ever, to understand how the series of program pulses works, you must first un- derstand how the algorithm applies a single program pulse. Table 3±1 outlines the steps involved in verifying programmed bits and applying a single pulse to each of the upper and lower bytes of a single location. This process corre- sponds to the steps enclosed in the dashed box in the flowchart in Figure 3±3.
Table 3±1. Steps for Verifying Programmed Bits and Applying One Program or Clear Pulse
Step | Action | Description |
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1 | Power up the VCCP pin. | Set the VCCP pin to VDD. If the VCCP pin for the flash module to be pro- | |||
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| grammed is not set to VDD, then the array will not be programmed. | |||
2 | Activate VER0 mode. | Set the VER0 bit in SEG_CTR (load SEG_CTR with 0010h). | |||
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3 | Delay for VER0 reference | The CPU executes a delay loop for the t | ² | ) | time period. |
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4 | Read flash array contents for | The CPU reads the addressed location. The flash module must be in | |||
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5Deactivate VER0 mode.
6Compare contents of flash location (16 bits) with de- sired data.
Clear the VER0 bit in SEG_CTR (load SEG_CTR with 0000h).
If the verification passes (i.e., if the data read in step 4 is equal to the de- sired data value), then no further program pulses are required. The flash word has been programmed with the desired data value. The program or clear function is completed and this algorithm is exited.
If the verification fails (i.e., if the data read in step 4 is not equal to the desired data value), then proceed to step 7.
PRELIMINARY | Algorithm Implementations and Software Considerations |