[sdiy] 7-segment LED displays with 4511 driver chip - max current?

rsdio at audiobanshee.com rsdio at audiobanshee.com
Mon Aug 17 03:46:49 CEST 2015

Hi Jason,

I meant to reply earlier to say that I like your idea below.

If an LED matrix needs to be interrupt-driven, then it would be possible to shift the next value into the shift register as the last operation of the interrupt, after which it could return immediately without a busy wait. The beginning of the interrupt would disable the old column, transfer the previous shift register value to the outputs, and then enable the new column. All of that can happen without wait states, usually, and the final operation would be to pre-load the next row. This adds very little latency and keeps the interrupt from looping to wait for completion of the serial transfer.

The only serious drawback is that the serial bus is not available for other communications without polling the "done" bit for the SPI/I2C. Slave select signals would be needed, too, but those are expected when sharing a serial bus.


On Aug 9, 2015, at 2:20 AM, Jason Tribbeck <jason at tribbeck.com> wrote:
> With the '595 you can shift the values in, and then tell it to transfer the shift register to the output register. This means you can pre-shift the pattern into the register, change the row, and then shift the pattern to the output.
> If you're clever with your design, you could make the row change and the output transfer use the same signal - so there would not be much in the way of delay. And if you're using SPI, then you could use the CS signal connected to the RCLK signal (which does the transfer) - it's a positive edge triggered input...

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