I am using an ATtiny88 in a pcb design. It is directly driving a LED matrix. I am only driving half bytes at a time, so the max current limit will be followed.

It is my understanding that I can dual purpose the icsp in the way that I have it. Since the ATtiny is driving the columns, when I go to program it, the reset pin is asserted, driving the pins tri-state, then allowing the iscp pins to be programmed.

Since the leds will be reverse biased while programming, they shouldn't cause any interference upstream.

Is this correct?

Also, the icsp labels go to a 6 pin programming header.

EDIT: Colums are the anodes, rows are the cathodes. It is a common cathode matrix.


  • \$\begingroup\$ For future reference, use the Atmel Appnote AVR042 - Hardware Design considerations. The answer to your question is in section 4.1.1. ww1.microchip.com/downloads/en/AppNotes/… \$\endgroup\$ Mar 21 '19 at 15:43
  • \$\begingroup\$ @KurtE.Clothier That's true, but my case was unique, and ended up not needed the series resistors as I predicted so that app note didn't help. \$\endgroup\$ Mar 23 '19 at 22:54

Just wanted to update this, as I had the PCB built and tested. The schematic above worked perfectly for programming, there was no issue with the SPI lines wrt the LEDs.


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