Calculating a delay/timer for 100 microseconds

[b_buerke]

Posted on January 17, 2005 at 08:19

Calculating a delay/timer for 100 microseconds

[b_buerke]

Posted on January 17, 2005 at 03:41

Hello i am using a st7lite29 and need a delay of 100 microsecond. Is this possible with the autoreloadtimer? I mean the 8-bit Timer B!!! Cause I dont exactly know how to calculate it! Is ther e anyone who can give me a hint??

Any help would be appreciated

Bjørn

[ This message was edited by: B_buerke on 17-01-2005 08:12 ]

[fggnrc]

Posted on January 17, 2005 at 08:19

Hello Bjørn!

You can measure a 100 us time with the LITE TIMER 2.

The max error is 32 main clock pulses, 'cause it is feed by the output of a 32 divider (see Figure 40 of the datasheet) whose value is unknown when your code starts measuring the delay.

If you can allow this error, these are the steps:

1) be sure that LTARR contains $FF BEFORE you start measuring the delay. If you plan to ''fire'' an interrupt when the delay will be timed out, disable it.

2) to start measuring a 100 us delay put 230 = 255-25 in LTARR (notice 100us = 25 * 32 clock pulses @ 8MHz)

3) if you plan to use interrupts, enable LTTB2 interrupt (set bit TB2IE in LTCSR2)

4) when the next LTCNTR overflow will happen (bit TB2F = 1 in LTCSR2), LTCNTR will start to measure the delay. This time is useful to restore $FF in LTARR.

5) when the next owerflow will happen, your delay is expired so you can do whatever you need.

I hope I was clear,

Regards,

EtaPhi