Help with simple PWM code

hey guys new arduino not microcontrollers. wrote simple program supposed fade pin 13 led. run program , see problem is? when use serial terminal view high , low time values start correctly once supposed switch direction start getting negative values. load , see if can figure out? thanks!

code: [select]

byte updown = 1;
int ht = 0;
int lt = 1000;


void setup()  {
 pinmode(13, output);
 serial.begin(9600);
}

void loop()  {
serial.println(ht);
serial.println(lt);
rep();
ht += updown;    //as high time goes lower low time same amount
lt -= updown;
if(lt == 0 || lt == 1000){
  updown = -updown;
 }
}

void rep()  {
 digitalwrite(13, low);
 delaymicroseconds(lt);
 digitalwrite(13, high);
 delaymicroseconds(ht);
}


quote

when use serial terminal view high , low time values start correctly once supposed switch direction start getting negative values.

negative values what?

a suggestion:

code: [select]

[glow]serial.print("ht = ");[/glow]serial.println(ht);
[glow]serial.print("lt = ");[/glow]serial.println(lt);


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