[sdiy] bizarre pic-midi issues

[Karl Ekdahl]

Ingo, Csaba;

I tried changing the resistor to a 1K but the 6N136 couldn't pull it all the way to ground, so i changed to a 2.2K which gives me the same results as before. However i did verify that the opto and everything works 'cause i connected it to a couple of gates to make a MIDI THROUGH and the synth at the end of that responded nicely.

So yes, there is indeed a problem inside the PIC however i'm still inclined to believe that the clocking is correctly set because
a) it works with MIDI OUT, and 
b) it gives me good data almost all the time while any setting higher or lower gives me framing errors all the time.

But regardless i could of course be wrong, please prove that it's so! :) I am inclined to believe at this point however that i indeed am dealing with a silicon bug, i noticed that this chip is a revision A3 which does have silicon bugs in its EUSART *but* none of the bugs mentioned in the six erratas i have are pertaining to asynchronous reception in 8-bit mode. Nevertheless, i placed an order with Mouser in the hopes of getting a never revision chip.

Karl

--- Den lör 2010-04-17 skrev Csaba Zvekan <czvekan at gmail.com>:

> Från: Csaba Zvekan <czvekan at gmail.com>
> Ämne: Re: [sdiy] bizarre pic-midi issues
> Till: Synth-diy at dropmix.xs4all.nl
> Datum: lördag 17 april 2010 22:18
> I use a 6n135 with a 1K pull-up and a
> 0.1µF capacitor to ground. It works like a charm . Ingo you
> have a valid point there . I still think his problem is
> clocking and settings.
> 
> 
> On Apr 17, 2010, at 10:02 PM, Ingo Debus wrote:
> 
> > 
> > Am 16.04.2010 um 20:19 schrieb Karl Ekdahl:
> > 
> >> The hardware i'm using is a PIC18F4550 connected
> with it's RX pin tied to pin 6 of a 6N136 via a 2.7K pull-up
> resistor,
> > 
> > In the Fairchild datasheet of the 6N136 propagation
> delay times are specified for a pull-up of 1.9k. Admitted,
> 2k7 isn't that much more, but maybe its worth a try using a
> smaller pull-up to speed up the optocoupler?
> > 
> > Ingo
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