currently I want to get an ATMega328P and an ATTiny85 to work on a breadboard, which should talk to each other and an LCD via TWI.
Anyway, I came across some issues I don't seem to be able to fix at all.
Without an ISP attached the ATTiny doesn't do a thing(programmed it to flash a light for now), connecting the ISP makes it work just fine. Similiar thing with the ATMega, when the ISP is disconnected I can't get correct data over USART. Either it stops transmitting entirely or some garbage is transmitted.
When I started I had a really barebones breadboard wired up, but as suggested in other forums and on here, I added a couple components in the hope to fix it finally.
Here's what it looks like right now:
Inititally I had a 4.7k as a pull-up on the reset pins, but it was suggested that 10k was better(with AVR circuit design considerations as source). Als the caps for the VCC/GND were added later on to reduce the affects of noise in the power delivery. The caps on the crystal were calculated with the spec sheet of it and a formula found in the ATMega spec sheet.
But nothing really helped. Even when I remove the ATTiny and have the ATMega on it's own, it won't really work.
Also it seems that the voltage on the reset pin is just 20mV. What could be the reason for that?
As a power supply I'm using a board called "ywRobot Power Board" plugged to a adjustable power plug which outputs 12V and can deliver 300mA max. The crystal is a 20MHz HC-49.
Fuse Bits on the ATMega328P: 0xFF/0xD9/0xEF(Ext/High/Low)(factory default, except clock-source and CKDIV8)
Fuse Bits on the ATTiny85P: 0xFF/0xDF/0x62(Ext/High/Low)(factory default)