Midi out problem

[John_Swenson]

I just put together a core module, checked out voltages, it looks fine. Put in the 18F452 I got from Smash already loaded with the boot loader.

When I setup midi-ox and turn on the core I don't get any messages. I tried a loopback on the PC- its working fine.

So I brought out the scope and looked at what was going on.  The oscillator is working fine, I get pulses out from the TX pin on the chip but they only go from ground to 1v. The VDD on the chip is 4.95V. In order to find out what was going on I disconnected it from the midi connections and just soldered various resistors across the midi out pins, making sure total current was never more than 10mA. What I found out was that the output pin high voltage was always 1v,  and the low value was always essentially 0v, no matter what the resistor from 5V to the TX pin.  

This doesn't sound like a normal output, either open collector or totem pole. It looks like there is a 1V zener across the output, but that doesn't make sense.

I tried three different processors and two of them gave this response, the other was different. When power was first applied it would go to 1V, then go to 5v for short time, then go back down to 1v and stay there, no pulses like the output from a UART like the other processors. But the output DID go to 5V for a brief period, which sounds like it IS something under program control.

This is very confusing, I don't see a software setable 1v output clamp listed in the datasheet .

Anybody have any clue whats going on?

Thanks,

John S.

[John_Swenson]

I found the problem, it was a solder bridge where the jumper to J10 is real close to the thin wire from TX, shorting pin 25 with pin 29.

With that cleared out I get nice full swing pulses, the PC can read the sysex commands.

Unfortunately MIOS still doesn't load, the data pulses are showing up at RD, but I only ever get the original sysex message out of it.  After each buffer I get a whole bunch of sysex messages, all the same as the original. After the download I keep on getting the message every 2 seconds or so.  I haven't tried any of the misi-ox settings yet, I'llgive that a try later on tonight.

John S.

[TK.]

Hi John,

fine that you finally found the error. :)

The upload won't work without the specific MIDI-Ox settings since burning data into a flash memory takes some miliseconds - read the instructions at the Bootstrap Loader page carefully for fast success ;-)

Best Regards, Thorsten.

[John_Swenson]

It turned out I wasn't putting in the processor specific ID into the syx file.

Since these are going to be lighting controllers mounted in walls and ceilings etc, I had separate IDs for each processor. Being able to program a specific processor in place by sending a midi stream into the network from one location was one of the main reasons I chose midibox for this system.

Once I got the right ID into the MIOS file it loaded fine, and I've assembled and loaded two different apps this morning, that do exactly what they were supposed to do!  Thats somewhat of an unusual experience, write the code, assemble it, load it and turn the knobs and push the buttons and the right stuff happens!! Way cool!

Now all I have to do is get the DMX converter working.  I'm modifying the midi-merger for that.

John S.