I made a PCB with ATmega2560. I mounted the AVR and a 16Mhz crystal oscillator with a feedback resistor and load capacitors. Also I mounted 0.1uF bypass capacitors (for VCC, AVCC pins). Then I tried to see if the chip can be programmed. Using AVR Dragon I applied 4.9V to my board and connected the ISP pins in my board to AVR Dragon. After that I tried reading Device Signature in Atmel Studio. However, I just see the error message 'failed to enter programming mode". Could one please suggest causes?
Some more details are below.
- The chip consumes 30mA from the AVR Dragon.
- In Atmel Studio the error persists regardless of ISP clock frequency. I tried down to 51Hz but it didn't solve the issue.
- With a scope I see that AVR Dragon generates SCLK, MOSI signals, but the MISO line is stable (a bit lower than 5V). It seems somehow the ATmega2560 does not respond.
- The voltages of XTAL1, XTAL2 are 0V. I'm not sure if it is normal or not. The chip that I use has never been programmed.
- I used a 100kohm pull up resistor for RESET pin. I don't have 10kohm and 4.7kohm, so I used 100k instead.
- I pulled up SPI_CS pin to 4.9V.