I actually made a prototype with multiplexing Chip select pin on Arduino, which connects to RESET pin of target board to program. When I am connecting one target board at once I am able to program it but when I am connecting multiple target boards then not able to program ICs.

I am using Nick gammon's code for programming the target Arduino using the master Arduino https://github.com/nickgammon/arduino_sketches/tree/master/Atmega_Hex_Uploader_Fixed_Filename

This is rough block diagram of multiplexing chip select pin -

I also tried connecting RESET pin of target Arduino to its chip select pin but that is also not working.

I actually made a prototype with multiplexing Chip select pin on Arduino, which connects to RESET pin of target board to program. When I am connecting one target board at once I am able to program it but when I am connecting multiple target boards then not able to program ICs.

I am using Nick gammon's code for programming the target Arduino using the master Arduino https://github.com/nickgammon/arduino_sketches/tree/master/Atmega_Hex_Uploader_Fixed_Filename

This is rough block diagram of multiplexing chip select pin -

I also tried connecting RESET pin of target Arduino to its chip select pin but that is also not working.

I actually made a prototype with multiplexing Chip select pin on Arduino, which connects to RESET pin of target board to program. When I am connecting one target board at once I am able to program it but when I am connecting multiple target boards then not able to program ICs.

I am using Nick gammon's code for programming the target Arduino using the master Arduino https://github.com/nickgammon/arduino_sketches/tree/master/Atmega_Hex_Uploader_Fixed_Filename

This is rough block diagram of multiplexing chip select pin - https://imgur.com/a/XX4Nyf8

I also tried connecting RESET pin of target Arduino to its chip select pin but that is also not working.

I actually made a prototype with multiplexing Chip select pin on Arduino, which connects to RESET pin of target board to program. When I am connecting one target board at once I am able to program it but when I am connecting multiple target boards then not able to program ICs.

I am using Nick gammon's code for programming the target Arduino using the master Arduino https://github.com/nickgammon/arduino_sketches/tree/master/Atmega_Hex_Uploader_Fixed_Filename

This is rough block diagram of multiplexing chip select pin -

I also tried connecting RESET pin of target Arduino to its chip select pin but that is also not working.