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Forum Index : Microcontroller and PC projects : CMM2: (Hsync?) screen glitches triggered by memory activity

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epsilon

Senior Member

Joined: 30/07/2020
Location: Belgium
Posts: 255
Posted: 01:01pm 24 Oct 2020
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Hi all,

I have noticed that my screen is a bit glitchy when a program is doing a lot of memory accesses. The glitches are horizontal, as if there's noise on the Hsync signal.
I'm in 800x600 8-bit mode, FW version 5.05.05.
The following short program is enough to show the issue on my CMM2 (I run it after a 'list files' or something like that so I have a screen full of text):


DIM x%(8000)
DIM ii%

DO
FOR ii%=0 TO 8000
x%(ii%) = x%(ii%) + 1
NEXT ii%
LOOP


With this I see glitches about once or twice per second. When I comment out the array access the screen is completely stable.
Are other people seeing this too, or this possibly due to my less-than-stellar soldering work?

Thanks for any help.

Ruben/Epsilon.
Epsilon CMM2 projects
 
twofingers
Guru

Joined: 02/06/2014
Location: Germany
Posts: 1124
Posted: 02:13pm 24 Oct 2020
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Hi Ruben,

I can't confirm that. Sorry!
My test code:
DIM x%(8000)
DIM ii%,a%=1

DO
FOR ii%=0 TO 8000
x%(ii%) = x%(ii%) + 1
if a% then  ? ii%;
NEXT ii%
a%=0
LOOP

Kind regards
Michael
 
mkopack73
Senior Member

Joined: 03/07/2020
Location: United States
Posts: 261
Posted: 02:44pm 24 Oct 2020
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Same, works fine on my CMM2 from Circuit Gizmos...

Did you clean the flux off the board after you finished soldering? Take some 90%+ IPA pour it on the board (front and back) and use a soft toothbrush to gently scrub the whole board. Then pour more IPA over it, then rinse it all off with water (distilled if you have it)... Then let it air dry for an hour or two.

Then see if you're still having the issues. Could be that there's just enough flux to give some connectivity between 2 pads.
 
matherp
Guru

Joined: 11/12/2012
Location: United Kingdom
Posts: 8518
Posted: 03:18pm 24 Oct 2020
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  Quote  I have noticed that my screen is a bit glitchy when a program is doing a lot of memory accesses.


Have you got an oscillator or crystal? If the latter then fit the former
 
epsilon

Senior Member

Joined: 30/07/2020
Location: Belgium
Posts: 255
Posted: 05:21pm 25 Oct 2020
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Thank you very much for the feedback guys!
I will try the oscillator mod and clean any residual flux.
It's the probably the crystal that needs to be an oscillator. Just looking hard at those two pads on the Waveshare seems to make it worse ;-) I'll reply here to confirm.
Epsilon CMM2 projects
 
epsilon

Senior Member

Joined: 30/07/2020
Location: Belgium
Posts: 255
Posted: 11:00am 30 Oct 2020
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Just a minor update: After switching back to OPTION FLASH, the issue disappears on my setup.
That reduces my motivation to try the oscillator mod a bit. The fact that not a single Belgian distributor seems to have a 0705 8Mhz 25ppm oscillator in stock doesn't help either. I don't want to pay $20 for the international shipping of a $2 part.
Epsilon CMM2 projects
 
Womble

Senior Member

Joined: 09/07/2020
Location: United Kingdom
Posts: 267
Posted: 11:20am 30 Oct 2020
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  epsilon said  The fact that not a single Belgian distributor seems to have a 0705 8Mhz 25ppm oscillator in stock doesn't help either. I don't want to pay $20 for the international shipping of a $2 part.

I seem to remember that the Oscillators I bought from Farnell UK came from their Belgian warehouse.

This is the part I used on the Belgian Farnell site LFSPXO018045 Oscillator, Crystal, 8 MHz, 50 ppm, SMD, 7mm x 5mm, 3.3 V, CFPS-73 Series

Hope that helps.

Womble
(aplologies if I picked the wrong language site, my French is poor, and my Flemish non existant)
 
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