DS1852 datasheet(24/26 Pages) MAXIM

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DS1852

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SCALING THE ADC

procedure writeTrimValue(trim :integer); (* write trim to part *)

procedure forceReference(Vin: real); (* applies reference voltage to input pin*)

procedure waitForNewConversion(); (* writes update byte to zero and waits for

update

of new conversion with present trim *)

function readValue():integer; (* reads converted digital answer *)

procedure ProgramTrim(trim :integer);(*enables EE for table3 & programs trim*)

Procedure calVad(maxInput :real)

var

Bit

:integer; (* counter - represents bininary bit 15-0*)

trim

:integer; (* present trim values *)

lsb

:real; (* the lsb value of the voltage reading *)

Vin

:real; (* the reference input voltage *)

Dec_in :integer; (* decimal representation of voltage input *)

Dec_out :integer; (* voltage reading in decimal *)

delta

:integer; (* present error of voltage reading *)

bestDelta

:integer; (* the error closest to zero *)

bestTrim

:integer; (* the trim that gave the best delta *)

Begin

bestDelta := 1000000;

bestTrim := 0;

trim := 4095; (* 0FFFh *)

lsb := maxInput / 65535;

Dec_in := 63888; (* input is ~97.5% of full scale *)

Vin := lsb * Dec_in;

forceReference(Vin);

(*Use SAR approach to trim course adjust on VAD scale bits 15-12*)

for Bit := 15 downto 11 do (* must go 1 bit too far so that zero is

possible solution *)

begin

if (Bit > 11) then

begin

trim := trim + lshft(1,Bit);

end;

writeTrimValue(trim);

waitForNewConversion;

Dec_out := readVoltage;

delta := Dec_out - Dec_in;

if ( delta >= 0 ) then

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