Discussion in "8051 Discussion Forum" started by    [email protected]    Oct 5, 2019.
Fri Oct 18 2019, 09:18 PM
Hopefully you understand some of the program.
Which parts don't you understand ?
Sat Oct 19 2019, 07:05 PM
sir, 3rd and 4th dot matrix display flickering,
Sat Oct 19 2019, 07:13 PM
please find video attachment. 3rd & 4th display flickering, and not scroll in their order, like 1 dotmatrix to 4.
Sun Oct 20 2019, 12:21 AM
Your code seems okay on my simulation
Try my code on your hardware.

Sun Oct 20 2019, 02:53 PM
sir, when i on display ,sometime 3rd display is not refreshing, i again switch off display, then it refresh.

Sun Oct 20 2019, 03:02 PM
sir, when i on display ,sometime 3rd display is not refreshing, i again switch off display, then it refresh.

[ Edited Sun Oct 20 2019, 03:03 PM ]
Sun Oct 20 2019, 03:09 PM
Thanks for support,

[ Edited Sun Oct 20 2019, 07:06 PM ]
Mon Oct 21 2019, 09:18 AM
I’ve been following this thread and looking at the example code and checking the MAX7219 datasheet. The code made sense and looked like it should work and I was ready to conclude some sort of hardware / timing problem between displays 2 and 3 when suddenly it clicked.

With four displays linked together data is effectively being clocked into a 64 bit shift register.

First 16 bits of DATA are sent then LOAD is strobed so the data is loaded into display #1.

Next 32 bits are sent (16=DATA, 16=NOP) and LOAD is strobed. The data is loaded into display #2 and display #1 gets nop.

However the original 16 bits for display #1 get shifted down the chain into display #3 so display #3 gets loaded with the display #1 data. It will briefly show a copy of display #1 until the actual display #3 data is sent which is why it flickers.

Data clocked into the shift register is not cleared after a LOAD pulse so 64 bits must always be sent to ensure all displays get loaded with NOP except for the selected display.

Something like:

    for x=4 to 1
        if x == displayNumber

[ Edited Tue Oct 22 2019, 12:42 PM ]
Tue Oct 22 2019, 05:18 AM

Thanks for support,

[email protected]


After Wimac's suggestion, I made a few changes.
Try this..

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