changing interrupt rates

i have a program that causes an LED on an 8051 controller to blink 5 times a second. here is what controlls the timer interrupt:

Code:

Timer3_Init (SYSCLK / 12 / 10);

using a system clock at 12 mHz, the timer will create interrupts at a 10Hz rate. How would i make it interrupt every 1/4 of a second?

A guess:

Code:

Timer3_Init ( (10 * SYSCLK) / 48);

thank you.

any guess on the effect of changing just the last number on the original interrupt?

Code:

Timer3_Init ( SYSCLK / 12 * 5 / 2 );

if you cant tell im totally new to C. i can find my way through C+, but this is all screwy so im going to have to disassemble existing code (with help from whoever wants to) to figure it out. and im using a silicon labs 8051fx20 IDE

im working with timers and interrupts to make a traffic light simulation. i want to alter some existing code to suit my needs.

ive changed the intial timing of the interrupt from 5 times a second:

Code:

Timer3_Init (SYSCLK / 12 / 10);

to

Code:

Timer3_Init (SYSCLK / 12 / 12);

in order to hopefully get 4 times a second (if 10 = 5 times a sec, then 50 = 1 sec, 50/4 = 12.5).

i am hoping i can use a delay or sleep function and just put it how many ms i want it to wait(to bypass all the machine cycle and timer overflow stuff), but i dont know if i can with the IDE.

i need to use the LED on the board (P1.6) as the green light, and use a series of while loops to switch the ports on and off.
ie: main street will use P1.0, P1.1, and P1.6 for the red, yellow and green respectively. side street uses P1.2, P1.3, and P1.4.

[psuedo]

Code:

while (delay <= 25000)
    turn P1.6 on
    turn P1.2 on
while (delay >= 25001)
    turn P1.6 off
    turn P1.1 on
while (delay >= 29001)
    turn P1.0 on
    turn P1.1 off
    turn P1.2 off
    turn P1.4 on
while (delay >= 54001)
    turn P1.4 off
    turn P1.3 on
if (delay > 58000)
    clear delay
    restart delay

[/pseudo]

if its possible to do what i want, how could i restart the delay and create an infinite loop?
if i cant use delay, then im stuck with machine timers and overflows...ugh

any insight is much appreciated

Go through the app notes. Try to find something on using the timer interrupts. Read up on whatever vendor documentation you can find about your Timer3_Init() function and its friends.

[edit]Also, here appears to be a more specific forum.

I am also very new at this and try to learn,

what if i want to change the interrupts of the LED each time i press a button....

i insert in the code: if ( p3,6 == 0 ) Timer3_Init (SYSCLK / 12 / 14);

else

Timer3_Init (SYSCLK / 12 / 10);

but it does not work......

i know it is very easy, can anyone help?