AN1711 datasheet(22/40 Pages) STMICROELECTRONICS

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SOFTWARE TECHNIQUES FOR COMPENSATING ST7 ADC ERRORS

value is taken equivalent to 18µs which is 2µs greater than the required time. This is chosen

precisely so that the 3rd conversion is not finished before we read the ADC data registers.

With a timer frequency programmed as 1MHz, the time for comparison is taken as 14. (4

values for 0xFFFC to 0x0000)

Comment

The results obtained from executing the ADC conversion in WAIT mode are more accurate.

This can be seen from the difference between the maximum value and minimum value re-

corded for an analog input (see Figure 12). However these results can still be affected by ex-

ternal noise.

3.4 EXECUTING CODE FROM RAM

The technique of executing the code from RAM can also be used to reduce noise. This is be-

cause the CPU does not access the Flash memory to fetch the op-codes but accesses RAM

instead.

The disadvantage of this technique is that you need spare RAM to act as program memory.

You have to load the ADC conversion function into RAM from the Flash or ROM program

memory at some known free RAM locations and then use the in-line assembly code to exe-

cute this function.

In the software example provided, we have used the STACK top memory to execute the ADC

conversion. The ADC conversion function is loaded in the STACK area at address 100h. The

size of the function is 8Bytes. We used these locations because stack-pointer never reaches

these locations in the application. Take care not to use lot of RAM, otherwise the STACK area

will be corrupted by the function and there could be un-predictable results.

AN1711 датащи(PDF) 22 Page - STMicroelectronics