Small 8x8 matrix driver?

Other Hardware LEDs and Multiplexing
41

CrossRoads:
Another advantage might be interface speed.
MAX7219/7221 can receive data at 10 MHz. I use mine at default SPI settings which I think is 4 MHz.
If your main processor was really tied up and you wanted to send stuff out at 8 MHz to get it out of the way quick. The master can do that, I think testing has has shown a 168/328 cannot receive that fast tho due to the slave having to sample (the CS pin?) or something along those lines.

Yeah, ideally that would be the way to go. But size and cost are really the most limiting factor.

42

a 168/328 cannot receive that fast tho due to the slave having to sample (the CS pin?)

True, when implemented poorly.

43

True, when implemented poorly."

False - max speed is a hardware function, not something users have any implementation control over:

"In SPI Slave mode, the control logic will sample the incoming signal of the SCK pin. To ensure correct sampling of
the clock signal, the minimum low and high periods should be:
Low periods: Longer than 2 CPU clock cycles.
High periods: Longer than 2 CPU clock cycles."

44

Still though, shouldn't 115200 baud serial be fast enough for this application?

45

Yes. The above was only discussing reasons why the ATmega is not always the clear way to go.
In this case, your need for overall thinness, similar cost, and no need for ultimate in interface speed indicates the Atmega is the way to go, as long as your time to develop the max7219 function is not factored in.

46

Gotcha. And yeah i'm still unsure 100% of how im going to go about implementing it...

47

A max7219 clone is fairly simple. You need to implement two basic elements:

  1. a display routine that is called from a timer isr to update the matrix in the background;
  2. an interrupt based spi slave.

The two pieces are integrated in the main loop where the incoming data (common + data bytes) are processed.

The beauty of this approach is that the execution in the main loop is non-critical and support the full capabilities of the spi hardware.

48

Thanks everyone for your responses, but in the end I will be changing the design around a little so that I can have slightly thicker parts and will be using the AS1130.

Cheers,
Nadav

49

That part drives nothing at all like an 8x8 matrix.
That part is also thicker than you said your requirement was.

What a waste of time.

50

CrossRoads:
That part drives nothing at all like an 8x8 matrix.
That part is also thicker than you said your requirement was.

What a waste of time.

No in fact it is thinner then the MAX7219, the SOIC package is only 2mm thick.
Also, I appreciate your answers but no one forces you to answer questions, if you feel its a waste of time, then you shouldn't do it. No one needs to hear about how you think you've wasted your time on this.