On Wed, Jul 29, 2009 at 12:47 PM, Steve Smith<xygax@blueyonder.co.uk> wrote:
> Tamas
> Thanks for the pointer...
> I am trying to get the whole thing inside a 3.5mm jack plug to convert a
> stream of data into IR at 455Khz... I have it working at 40Khz but the da=
ta
> rate is far too slow...
>
> I could get away with 250Khz but there dosen't seem to be any receivers
> rated to that they are either 56K or 455K I have been looking at the
> TSOP7000 as an RX optimised around 455K
>
> STeve
>
>
> -----Original Message-----
> From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On Behalf =
Of
> Tamas Rudnai
> Sent: 29 July 2009 18:30
> To: Microcontroller discussion list - Public.
> Subject: Re: [pic] a tight code chalenge 455Khz burst...
>
> Hi Steve,
>
> I think the situation is a bit worse. First of all you need 4 instruction
> cycles, not 4 instructions... GOTO takes 2...
> Secondly, 455kHz means you need to toggle the port bit at every 2nd cycle,
> not every 4th.
>
> If a little glitch is acceptable you may can try something like this:
>
> LOOP:
> =A0BSF =A0 GPIO,outbit
> =A0BTFSS =A0 =A0GPIO,inrxbit
> =A0BCF =A0 GPIO,outbit
> =A0BTFSS =A0 =A0GPIO,inrxbit
> =A0BSF =A0 GPIO,outbit
> =A0BTFSS =A0 =A0GPIO,inrxbit
> =A0BCF =A0 GPIO,outbit
> =A0BTFSS =A0 =A0GPIO,inrxbit
> ...
> ... doing this for a while makes a continuous signal
> ...
> =A0BSF =A0 GPIO,outbit
> =A0BTFSS =A0 =A0GPIO,inrxbit
> =A0BCF =A0 GPIO,outbit
> =A0BTFSS =A0 =A0GPIO,inrxbit
> =A0GOTO =A0 LOOP ; glitch occures!
>
> =A0GOTO =A0 MAIN
>
> But I think you should go for a mid-range device instead where you have
> interrupts and PWM module as Dario suggested...
>
> Tamas
>
>
>
> On Wed, Jul 29, 2009 at 5:56 PM, Steve Smith <xygax@blueyonder.co.uk> wro=
te:
>
>> Guys:
>> During a program I have to periodically make a burst of 455Khz pulses and
>> stop when a pin changes state....
>>
>> Using an pic 12F510 I can get an 8Mhz internal osc that gives me about 4
>> instructions to manufacture this burst and sense the end. It goes
> something
>> like this
>>
>> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0Code =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =
=A0 =A0 =A0 =A0 =A0cycles (500ns )
>> =A0 =A0 =A0 =A0Bsf =A0 =A0 GPIO,outbit =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =
=A0 =A0 ;0 =A0 =A0 =A0 =A0 =A0 =A0 =A06
>> =A0 =A0 =A0 =A0btfss =A0 GPIO,inrxbit =A0 =A0 =A0 =A0 =A0 =A0;1
>> =A0 =A0 =A0 =A0goto =A0 =A0main =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =
=A0 =A0 =A0 =A0;
>> =A0 =A0 =A0 =A0bcf =A0 =A0 GPIO,outbit =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =
=A0 =A0 ;3
>> =A0 =A0 =A0 =A0goto =A0 =A0$-4 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =
=A0 =A0 =A0 =A0 ;4
>>
>>
>> best I can do is 5... Anybody got any better ideas I am trying to get a
> one
>> chip solution in the smallest possible space and it needs a comparator
>>
>> TIA
>>
>> STeve
>>
>>

The PIC is the wrong solution.  Just build a gated RC oscillator out
of a dual comparator (since you say you need a comparator).

Regards,
Mark
markrages@gmail
-- =

Mark Rages, Engineer
Midwest Telecine LLC
markrages@midwesttelecine.com

-- =

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