"unable to enter programming mode" after fuse configuration

Hey there,
Basically, I am programming a serial port UART connection. It was not working properly even in proteus. The problem that I have found is that the baud rate settings generated by the serial_set_baud_rate function is intended for 20MHz oscillator. The fuses were configured in my the 3pi so that it uses internal oscillator with speed lower than 20MHz sure. So I configured the LOW byte fuse to 0xE0 as I referred to ATmega328P manual (Before LOW fuse was: 0xF6). The ISP programmer is still able to connect to other 3pi robots.
I did not change anything for DWEN fuse
Please hElP!


The 3pi is by default configured to run at 20MHz. From looking at the ATmega 328P datasheet, the fuse setting 0xF6 for CKSEL3…0 should set the microcontroller to use the Full Swing Crystal Oscillator. Changing those fuse bits to 0xE0 would change it to use the External Clock. That is probably why you are not able to connect to it. At this point the only hope of recovering this 3pi is to try supplying an external clock signal to pin PB6. However, I do not know if this will work given that that pin is already connected to the resonator.