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CALIBRATING THE RC OSCILLATOR OF THE ST7FLITE0 MCU USING THE MAINS

4 SOFTWARE EXAMPLES

A zip file attached to this application note contains the complete software of this calibration

method.

4.1 SINGLE ALTERNANCE

This version perform only one count between two edges and changes the value of the RCCR

according to this measurement. This can lead to bad tuning if there is noise on the reference

signal.

4.1.1 main program

;All the bytes from locations 80h to 85h 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

$83

;these two bytes contain the two 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

$84

;this byte contains the number of counter overflows

during the measurement

;control register

.cr

equ

$85

;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

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

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

srl

value

;dichotomy value divided by 2

ld

A,#$F9

;these lines calculate this equation:

ld

X,nbover

;

mul

X,A

;(nbover*$F9)+ capture2 - capture1

add

A, capture2

;