I dropped the pullup resistor to 150, then 83 ohms and it has made no
difference. I cannot change the 660 ohms bit as that is coming from the midi
out of my synth. Here is what it says in the midi spec...

'The MIDI circuit is current loop, 5 mA. Logic 0 is current ON. One output
drives one (and only one) input. To avoid grounding loops and subsequent
data errors, the input is opto-isolated. It requires less than 5 mA to turn
on. The Sharp PC-900 and HP 6N138 optoisolators are satisfactory devices.
Rise and fall time for the optoisolator should be less than 2 microseconds.'

Maybe I should give up and try and get hold of a 138? ( I know somebody has
done it with a 139 as I found a reference to it on the web - only no
schematic : damn!)

Thanks for the help..
Catchy



-----Original Message-----
From: Joe Little <Joe.Little@SCIATL.COM>
To: PICLIST@MITVMA.MIT.EDU <PICLIST@MITVMA.MIT.EDU>
Date: 18 May 1998 14:25
Subject: [Re:] Midi in to PIC problems


     The 6N138 and 6N139 are very similar.  They even share the same page in
the
     databook.  I noticed only a small difference between the two.  The '139
can
     withstand a little more voltage on it's output, and it is a little more
     sensative on it's input.... but it's a little slower passing the
signal.

     I noticed that they run a little faster when driven a little harder.
The
     input can stand 20 mA continuous drive, and Pin 6 may sink 60mA
(Absolute
     maximums).  For 5V systems, the series resistor on the input may be
reduced
     to 250 ohms.  Notice that there is 660 ohms from three resistors there
now.
     The pullup resistor on pin 6 may be reduced to 83 ohms.

     You could try reducing the resistor values toward the minimums to see
if it
     fixes the problem.

     joe
     jlittle@mindspring.com

     ----------------------------
     Hiya,
     Can anybody help me? (no smart comments please :-)

     I am trying to get MIDI data into my 16C77. It kind of works, but seems
to
     get some wrong values through (I have examined the same stream on the
PC
     and it is being transmitted correctly)

     PIC is running at 10 Mhz (oscillator using 22pf capacitors). SPBRG is
set
     to 4 (which should give me the 31250 bps right?)

     The circuit I am using for input is basically a standard circuit (see
the
     input section of http://www.borg.com/~jglatt/tech/midi.gif ), but I am
     using a 6N139 opto isolator (because I cannot easily get hold of a
6n138).

     I would imagine that there is a slight difference that I need to get
over
     but
     1) I have no specs for the 138 to compare with 2) My analogue
electronics
     is pants

     has anybody got any ideas I could try (like maybe a new hobby :-)

     Regards
     Catchy