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Subject: Re: LED flickering problem
Date: Mon, 23 Dec 2002 20:02:16 +0100
References: <firstname.lastname@example.org> <email@example.com>
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On Mon, 23 Dec 2002 15:04:47 GMT, Spehro Pefhany
>On Mon, 23 Dec 2002 09:03:48 +0000 (GMT), the renowned Tony Williams
>>In article ,
>> Spehro Pefhany wrote:
>>> It's a multiplexed situation..
>> Any chance of an interrupt disturbing the scan?
>That's what I suspect- or it may not be disturbing the scan
>directly but screwing with the DDR registers or something of
>that ilk. Or maybe the scan is being done by interrupts and
>something is turning the interrupts off for too long (less than
>10% or so jitter won't be noticed). There are far too many
>ways to do something like this wrong to enumerate.
Bingo - I would go for interrupts too. Make scanning an
uninterruptable process with rigid timing. It is remarkable what
little timing shifts become visual already.
In a project that included many I2C communication processes and
keyboard scanning we did keyboard scanning parallel with LED
multiplexing (same row or column signals used for digit switching),
and after the whole display scan a rigidly fixed display "dead" time
window was reserved for other processes and communications.
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