MidiboxPlus (Sometimes they come back)

Antix · October 13, 2016, 9:09pm

hi,

Recently I bought a JX-8P and decided to program it with a nice looking MidiboxPlus ( no matter the age :))

I am using:

16F877-20/P

20 MHz xtal

mplus_pcb_v1.brd redesigned board which is consistent with the final schematic

succesfully burned and verified PIC with ME-Prog from Micro Engineering using Epic Programmer ( I made a lot of Midibox with this programmer )

midibox_plus_v1910.zip is the firmware with the 16 pot variant

now the pain

I powered up about 50 or 60 times and LCD visualized the right screen only 3 times. ( as you can see in the attached image )

the other times a line of blank character .

It seems to me something like a bad LCD initializing ( am going to buy another LCD in the case the one I have may be too slow)

Please does anyone reported strange behaviour like this on MidiboxPlus or other possible cause of malfunction? ( I am searching in the forum but have not a solution yet )

Thanks for any help or information

Best regards

Antonio

P.S.

I am going to buy new LCD from different manufacturers but if someone reported of slow LCD ( initializing ) please I will be glad for any help

T.K · November 2, 2016, 10:03pm

Do other readers: MIDIbox Plus is not a MIOS based firmware.

This information is only relevant for PIC16F based designs that I published ca. 13 years ago

@Anitix: could you please check if the power-up timer is enabled?
-> http://microchip.wikidot.com/8bit:pwrt

Without this timer it could be that the display initialisation starts too early for your LCD

Best Regards, Thorsten.

Antix · November 5, 2016, 6:25pm

Thanks Thorsten for your reply

as usual you are very kind

Often the more you break your head on the wall the more simple is the solution of the problem

After a lot of evening trying to make work my circuit I noticed that the problem is the programmer and the 16F series.

I made a lot of midiboxes with my programmer without any problem but 16F877 wants Vdd during programming

and as you can see in the schematic the “P” ( programming ) position cuts Vdd. ( the “E” position is for evaluation board function )

With Pic 18F452 or 4620 or 4685 I never had this problem an succesfully programmed in P position

Probably I am a stupid and forgive me if all of you already knows that 877 needs Vdd during the programming but may be useful share this information about older PIC.

I was deceived from the random operation , as you can see the picture the circuit worked occasionally.

Thanks again to TK

Best regards

Antonio