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CALIBRATING THE RC OSCILLATOR OF THE ST7FLITE0 MCU USING THE MAINS

4.2 AVERAGE VERSION

This version perform the count between two edges four times and changes the value of the

RCCR according to the average of these measurements. This method allows to perform a

better tune of the RC oscillator.

4.2.1 main program

;All the bytes from locations 80h to 8Bh are used by this software to store values or as control

registers but they can be reused safely after the clock has been set.

;dichotomy value

.value

equ

$81

;this byte contains the value which will be added

or subtracted to/from the RCCR last value at the end of each round

;capture values

.capture1

equ

$82

.capture2

equ

$86

;these bytes contain the values of the counter captured

on the edge of the mains, they are used to calculate the time elapsed between the two edges

;number of overflows

.nbover

equ

$8A

;this byte contains the number of counter overflows

during the measurement

;control register

.cr

equ

$8B

;this byte is used as a control register for the measure-

ment. Its bits allow or not the interrupts and show which step of the count is the current one.

.strtstp

equ

1

;this is set to start the count and reset to stop it

.overflow

equ

2

;this bit is set when the first capture has occurred. It

allows the overflows to be counted

.main

bset

MCCSR, #1

;output clock enable. You can remove this line if you do

not want to check the clock frequency

ld

A, #$80

;value containing the value which will be

ld

value, A

;add or subs to/from RCCR during the dichotomy

ld

RCCR, A

;RCCR is set to the middle of its range of value

next

clr

nbover

;clear the byte containing the number of timer overflow

clr

cr

;clear the byte use as control register for the count

ld

A, LTICR

;clear the ICF bit

clr

Y

capture rim

;interrupts enable

bset

LTCSR, #7

;enable input capture interrupt

bset

cr,#strtstp

;set the start-stop bit of cr: count can start

count

btjt

cr, #strtstp, count; wait for the end of count

clr

LTCSR

;lite timer interrupts disable

inc

Y

cp

Y,#$4

;repeat the capture four time to make an average

jrne

capture

srl

value

;dichotomy value divided by 2

clr

Y

ld

A,#$F9

;these lines calculate this equation for the four

ld

X,nbover

;measures:

mul

X,A

;(nbover*$F9)+ capture2 - capture1

calcul add

A, (capture2,Y);

jrnc

nocarry

;this equation is calculated with 16 bits

inc

X

;