MEGA2560 Boot up problem


I am using a Mega2560 and setting bits 22 through 35 as outputs.
Everything works fine except during boot up, they all go HI and then low.

This is causing problems with my other board that is being controlled by
the MEGA2560. The BITS 22-35 connect to 74LS374 chips.

During MEGA2560 boot up, the 74LS374 chips cause wrong outputs becasue
the outputs go HI.

I have tried, 10K, 5K, and even 1K pull down resistor to stop them from going HI during
Boot Up. It did not help.

I even made them INPUTS pins instead of OUTPUT pins in the setup and then
change them to OUTPUT pins. It did not help.

I do not think any user programming will help becasue the logic cycle happens before
my program is even starts.

Any help would be appreciated.



Wrong logic family?

The Arduino pin is high impedance during bootup, but the 'LS' inputs default to HIGH.

Try the 'HC' logic family.

As bahram states change the chip to the 74HC374, then you can add pull down resistors to the outputs and when you are ready you select the chip. The chip select is an active low so it will be deselected until your code turns it low.

Good Luck & Have Fun!