Two 4x 7219: Scroll starts on BOTH displays rather than continuous

Projects General Guidance
1

Hi,
Using two 4x 7219 displays with UNO have been working perfectly. Starting at one end and scrolling through all eight 8x8 matricies.

On the unit that was working fine, I just opened it up to replace one 8x8 matrix....it was brighter than the other 7....I had mixed and matched 8x8's when I built it. So now I wanted to put back one with the same brightness.

Result is:
a) all now match in brightness

b) Scrolling starts ON EACH set of 4 matricies, so Hello World is scrolling concurrently rather than continuously.

I assume my sketch is not the problem, and something I did when I opened it up caused the simultaneous scrolling. I tried unplugging and replugging, and resetting. Still the same.

Does anyone have a suggestion as to what may be the problem?
Thank You

2

Forgot to mention. I did not change any pin arrangements. Just simply re connected the jumpers.

3

Disconnecting and connecting makes a physical exercise for the cables and connectors.
To pinpoint any cable You would need to supply schematics and links to the display modules.
Please clarify the fault description. Show the display before and after a shift.

4

Hi Railroader,
Thanks for your post. I do so appreciate those on the forum.

I figured out my problem..........I was WRONG when I said "I assume my sketch is not my problem"

What happened was, after I finished replacing the 8x8 matrix, I opened "the sketch"......and it caused the problem of simultaneous set of scrolling.

Since then, I just noticed I had a 2nd sketch saved with similar "but not the same sketch name".

For the heck of it, I tried that one and IT WORKED.....

I couldn't figure out why it worked and the first one didn't. So I decided to COMPARE LINE by LINE the 2 sketches.......and found the problem

1st Sketch had #define MAX_DEVICES 4

2nd Sketch which was actually my later sketch had
#define MAX_DEVICES 8

Then....as a test, I ran a sketch with
#define MAX_DEVICES 2

And it had multiple sets of 2 matricies scrolling concurrently.

Bingo....I confirmed the solution which is:
...Make sure I define the CORRECT number of devices.

Hopefully this may help others who had a similar problem.

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