Hi friends. This forum help me a lot in my search of speeding I/O with Arduino. Now I will share something that I found that I did not see posted before. Although the maximum speed at which a bit can be toggled should be 2.67 MHz, with this simple routine I could reach 8 MHz: For example, for toggl…

On an ATMega Arduino try this, which also toggles bit 2 of PORTC: cli(); byte i=0; for(i = 0; i < 4; i++) PINC = 4; Also try eliminating the loop, and inlining as many "PINC = 4;" statements as you want. Check the ATMega data sheet to see why this works.

Hi Jremington. I see this. You say that for small loops the compiler is using these opcodes and that's why my code works at 8 MHz ?

A statement like: PORTC = 0x22;is translated by the compiler directly into one or two machine instructions and is much, much faster than using digitalWrite(). The technique is called "direct port access" in the Arduino world.

Oh, yes ! I already knew that, and that's why I did not use digitalWrite. But I have read in at least 4 different places (including many posts on a thread at this forum) that the maximum speed in such a direct port addressing way was 2.67 MHz, given the number of clock cycles needed for each I/O in…

You can probably make it faster by hanging your for loop to for(byte i = 4; i;--i) {} That way, the for condition becomes a check for zero - the compiler does not have to subtract 4 from the number to do the check. Note also that I use a predecrement operator. It probably doesn't matter here, but …

For small loops, the compiler is "unrolling" your loop, producing: 96a: f8 94 cli 96c: 96 e2 ldi r25, 0x26 ; 38 96e: 98 b9 out 0x08, r25 ; 8 970: 82 e2 ldi r24, 0x22 ; 34 972: 88 b9 out 0x08, r24 …

Input-Output as 8 MHz

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Input-Output as 8 MHz

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