AN1353

Main program

Rev 2

5/17

3.3

Start-up and smart reset

At each RESET interrupt, the program first checks if the data stored in the RAM are as

scheduled or not. In-deed, a RESET can occur without the supply voltage having fallen

below VRM (Data retention parameter: 0.7 V). In this case, a whole start-up is not

necessary, and the program can keep working with the previous RAM data. This is helpful in

order to avoid missing loads control when a RESET occurs, due to an EMI problem for

example.

If the checked RAM registers are not as expected, then a complete initialization procedure is

launched (see Appendix B). This routine, among other things, configures the A and B ports,

waits 100 ms before go on (wait-ing for the stabilization of the supply), and measures the

mains period for the first time.

If the RAM area is adequate, then a “Smart Reset” can be performed. Only the registers

which are used to store internal sub-routines variables are cleared. Only the main registers

keep their previous values (motor status, etc.).

It is important to note that this start-up procedure can miss firing some loads during one

mains cycle. This is why, if the motor was at start-up state before a “Smart Reset”, it is better

to stop the motor. This avoids switching both the Tr and Ts devices ON together when the

split phase capacitor can be charged (refer to AN1354). This is done by simply setting to

high level the overcurrent detection flag.

Table 4.

CPU available time

Name

Duration

(ms)

Code execution time

(ms)

Subroutines time sum

(ms)

Available time (ms)

T1

0.45

0.25

0

0

T2

1.05

0.13

0

0.72

T3

1.75

0.13

0

1.42

T4

3.95

0.85 (T50 Hz average)

1.75

1.15

T5

2.80

0.09

0.26 + 0.92

1.33

DELTAT

6.75

0.08

5.49 + 0.93

0

TOTAL

4.62