Hanging Notes

[goyousalukis]

Hello, I hope someone can help me. I have built the midibox 16, and it works great - except for one thing: when I use it between my software analog sequencer emulator and my synth module, I often get hanging notes, as if the noteoff midi message got deleted. This happens when I make rapid movements on two of the sliders I use - specifically for the filter resonance and frequency. Is there a fix for this? Is there anything I can check? Thanks for any help...

Justin

[TK.]

Hi Justin,

unfortunately this is a known problem with MIDIbox Plus. The root cause is the 4-bit LCD interface without read signal. Since the MBPlus firmware is not able to ask the LCD if a character has been printed out or not, it has to wait for a certain time before continuing with the main program. If a lot of MIDI events are received continuously, the LCD delay routine will be interrupted very often and therefore takes much longer than expected, as a result the whole display update takes more than 300 uS and this can cause a MIDI buffer overflow on a back-to-back MIDI event stream.

This issue has been fixed on all MBHP designs by accessing the LCD over a 8-bit interface and by polling the busy flag of the LCD.

For MPlus two workarounds are possible: if you don't use a display, I could give you a special version which doesn't try to access the LCD.

If you own a LCD, I've to include some code which is also used by the MB1664 variant. This variant would require a hardware modification (read-line has to be connected with the PIC)

Best Regards, Thorsten.

[goyousalukis]

Thorsten, thanks for the reply. I plan on building a full blown MB64 in January, so I guess I will just wait until then. Your project is great! Thanks...

Justin