When using Internal Clock 8MHz, timming is uncorrect

Other Hardware 3rd Party Boards
1

Hello, Arduino Forum.

i need your help to solve this problem.
that is timming is incorrect, when i use internal clock 8MHz.
make and using custom mega2560 board,
all function and upload well, but only timming is incorrect.

use this library : "GitHub - MCUdude/MegaCore: Arduino hardware package for ATmega64, ATmega128, ATmega165, ATmega169, ATmega325, ATmega329, ATmega640, ATmega645, ATmega649, ATmega1280, ATmega1281, ATmega2560, ATmega2561, ATmega3250, ATmega3290, ATmega6450, ATmega6490, AT90CAN32, AT90CAN64 and AT90CAN128"

is there are any setting code i need?

no need very high speed clock,
9600bps softwareSerial, Max 3.3KHz Buzzer PWM

this is my issue links in github

We invite you to share your knowledge.
thank you

Best Regrads

2

You need to burn the bootloader to the atmega2560 chip, with the frequency set to Internal 8MHz in the IDE tools menu. Even if you choose "No bootloader", you still need to burn the bootloader to set the fuses correctly for 8MHz.

3

Why SoftwareSerial? The atmega2560 has four hardware serial ports.

4

Thanks for kind reply @daved_2018.

unfortunatly i connected Rx Tx crossed,
and already make pcb boards haha...

that's why i use swserial to set Rx/Tx pin crossed

5

PCB patch with 2 carves and 2 little wires?

6

Thanks for help @buckfast_beekeeper :slight_smile:

First of all, we only check whether the function works, and if there is no problem, we plan to make a new PCB.

It's meaningless if it doesn't work.
haha..