Unixtime.SCL

// Convert system time to unix time
// (seconds until 1970-01-01 00:00)

FUNCTION Unixtime : DWORD 

VAR_INPUT
END_VAR

VAR_TEMP 
leapyears       : INT;
days_from_1970  : DINT;
days_from_BeginOfYear : ARRAY[1..12] OF INT;
l_unixtime      : DINT;
sfc1_ret_val    : INT;

CDT_systemtime  : DATE_AND_TIME;

systemtime AT CDT_systemtime : STRUCT
    year_CDT            : BYTE; // 1970 ... 2038
    month_CDT           : BYTE;
    day_CDT             : BYTE;
    hour_CDT            : BYTE;
    minute_CDT          : BYTE;
    second_CDT          : BYTE;
END_STRUCT;

year        : INT; // 1970 ... 2038
month       : INT;
day         : INT;
hour        : INT;
minute      : INT;
second      : INT;
END_VAR

leapyears     := 0;
days_from_1970  := 0;

// days of current month without leap day

days_from_BeginOfYear[1]  :=   0;  
days_from_BeginOfYear[2]  :=  31;  
days_from_BeginOfYear[3]  :=  59;  
days_from_BeginOfYear[4]  :=  90;  
days_from_BeginOfYear[5]  := 120;  
days_from_BeginOfYear[6]  := 151;  
days_from_BeginOfYear[7]  := 181;  
days_from_BeginOfYear[8]  := 212;  
days_from_BeginOfYear[9]  := 243;  
days_from_BeginOfYear[10] := 273;  
days_from_BeginOfYear[11] := 304;  
days_from_BeginOfYear[12] := 334;  


// read system time
sfc1_ret_val    := READ_CLK(CDT := CDT_systemtime);
year            := BCD_TO_INT(systemtime.year_CDT) + 2000;
month           := BCD_TO_INT(systemtime.month_CDT);                       
day             := BCD_TO_INT(systemtime.day_CDT);
hour            := BCD_TO_INT(systemtime.hour_CDT);
minute          := BCD_TO_INT(systemtime.minute_CDT);
second          := BCD_TO_INT(systemtime.second_CDT);


// sum of leap years since 1979 (without current leap year)
leapyears := ((year-1)-1968)/4      
           - ((year-1)-1900)/100
           + ((year-1)-1600)/400;
                            
                  
days_from_1970 := (year-1970)*365 + leapyears
                   + days_from_BeginOfYear[month] + day-1;

IF ( (month > 2) AND ((year MOD 4 = 0) AND ((year MOD 100 <> 0) OR (year MOD 400 = 0))) ) THEN
    days_from_1970 := days_from_1970 + 1; // + leap day, if year is leap year
END_IF;

// OUTPUT in s
l_unixtime :=  second + 60 * ( minute + 60 * (hour + 24 * days_from_1970) );


// if error return 0
IF  sfc1_ret_val <> 0 THEN
    Unixtime := 0;
ELSE      
    Unixtime := DINT_TO_DWORD(l_unixtime);
END_IF;


END_FUNCTION