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Consider I have 4 daised chaining of MX7219 LED Matrix 8×8. Thats mean i have more width than height (32×8) or (width×height)

If i want improve overal width of LED again, thats mean i must continue daisy chaining from DOUT of previous module to DIN pin of new module so i will have (40×8).

If i want improve overal LED height so i can have 32×16, I have two options, I can define new CHIP SELECT pin of SPI in my microcontroller, or I can continue daisy chain.

Which one better?

Muhammad Ikhwan Perwira
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  • Who can say? Wouldn't this depend a great deal on what you value? The only thing we can say is that extending the daisy chain means either increasing the frequency or else taking longer to update. – jonk Apr 18 '22 at 07:41
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    If you have only one SPI bus, then you will still only be able to write to one at a time anyway, so is there any advantage in adding another chip select? – HandyHowie Apr 18 '22 at 08:36
  • I suppose one faulty chip will take less of the display down if you have multiple chip selects. – HandyHowie Apr 18 '22 at 08:40

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Using two CHIP SELECT pins may have an advantage.

When you use a single CHIP SELECT pin, you have to rewrite the full daisy chain even if you want to change only a few bits.

When you use two CHIP SELECT pins, you can change a few bits by rewriting only the daisy chain containing the bits to change and don't write the other one with no changes.

Depending on your use of the LED display, it may be better to use four CHIP SELECT pins instead of one or two.

So I would measure the time for a full rewrite of the a single long chain. If this time is so long that a display update would be too slow, I would consider several CHIP SELECT pins.

Uwe
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