AN1812 datasheet(31/34 Pages) STMICROELECTRONICS

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AN1812

13 References and bibliography

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Appendix D Software flow

The fCPU chosen is 8 MHz. Koffset and Kgain are calculated by taking the reading for two known

inputs. The flow of the software, use to implement the algorithm, is as follows:

First the I/O pins, Timer, SCI (Tx @ 9600 baud rate) and some global variables used in the

ADC are initialized.

Then a string is transmitted to check that SCI is working fine.

The settling time is kept fixed at 1 second for fCPU = 8 MHz.

Some initial readings are taken and ignored while the ADC stabilizes.

The control enters an infinite loop.

Inside the infinite loop, there is a loop in which ADC captures the timer values 17 times.

But the first reading is ignored.

The remaining 16 captured values are converted into the corresponding voltages (up to 10

µV precision) and then transmitted a PC for display by the Hyperterminal after being

converted into a buffer of ASCII characters.

The average of 16 timer readings is taken and sent to the Hyperterminal as a time value

and a corresponding voltage in the same manner as described above.

The difference between the maximum and minimum captured value is also sent to the

Hyperterminal in the same way as in step 8.

10. After this step, the software enters an ‘IF’ loop “if (mCount == 18)”, where the ADC is reset

in order to measure the next input value. Again a few readings are ignored while the ADC

stabilizes. The counter and other global variables are also initialized.

11. After this, the software re-enters the loop of 17 conversions and executes step 6 to step 9.

This process continues until you reset the system manually.

D.1

Code size

The software given is for guidance only. Here the display is done for up to 10 uV precision. You

can modify and use your own code for the display of the data. The following table summarizes

the code size. Depending on the compiler and memory placement, these values can change.

The RAM requirements are not provided and you have the choice to place the variables as

global or local.

Table 4.

.Code size

No.

Function Name

Code size

( Bytes)

ADCSys

Acquisition

128

Start_Capturing

Reset_ADC

ADC_InitializeVar

IsCaptured

Delay_Second

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