Question about 8253-timer channel 2 
Author Message
 Question about 8253-timer channel 2

Hi,

I've tried to read the current latch-value of the
channel 2 to determine current speaker-frequency
without success. The value varies. Seems that
I've read the value of the running counter.

Would anyone tell me how I could do this correctly?

Thanks.
--
/*  Nan-shan Chen, Uni. Paderborn, Fachbereich 14
    Pohlweg 47-49, 33098 Paderborn, Germany       */



Thu, 27 May 1999 03:00:00 GMT  
 Question about 8253-timer channel 2

Quote:

> I've tried to read the current latch-value of the
> channel 2 to determine current speaker-frequency
> without success. The value varies. Seems that
> I've read the value of the running counter.

On both 8253 and 8254 it is write-only (you can latch
and then read actual counter value, not the programmed
limit). On 8254 only, you can get counting mode using
Read Back command (MOV AL,0E8h; OUT 43h,AL; IN AL,42h).
The only ways to determine the frequency are: 1. measure
the time between pulses; 2. read all values...


Fri, 28 May 1999 03:00:00 GMT  
 Question about 8253-timer channel 2

I don't have a data book in front of me now, so I'm not sure what the
exact port location is, but you can send a latch status command to port
43h.  The next read of the timer 2 port returns some info on timer 2's
mode.  One of the bits (bit 6 I think) is the NULL bit, which indicates a
new value just got loaded.  After this bit gets set, you can immediately
read the timer count and it will be pretty close to the count.



Thu, 03 Jun 1999 03:00:00 GMT  
 
 [ 3 post ] 

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