Right... I was refering to a situation I had once where I had a relay connected to MOSI and during programming, the relay kept clicking like mad. Hence were I got the berserk adjective. The buttons are normal push to make buttons which do not have to be pressed during programming. It is understood that by doing so, I would be interfering with the programming but this is better than having a relay or some output connected to them and during programming you would be risking damaging or controlling something.
So, is that means it is better not to connect any input/output device at the MOSI, MISO and SCK pins ? Are you programming using USBasp/usbtiny right ? If you are using ftdi programmer, then it will only involve Tx and Rx
It depends what you are doing. On the Uno the Tx/Rx pins are connected to the USB chip and have pull-ups on them, making them not particularly useful as input pins.
Also if you put a load on them you may not be able to upload a new sketch until you disconnect it. This may or may not bother you.
Let's not get bogged down here. Possibly that line could be omitted, but if you make a stand-alone version (without the USB chip) then you would need it.
Yes this only makes sense when using USBtinyISP.
I need to learn more on SPI... Actually I have difficulty making a distinction from
UART - This is a Tx -> Rx & Rx -> Tx single device connection right? I2C - As for as I know, this is a 2 wire protocol which can accept a maximum of 255 channels and any device connected to the same channel gets the message sent SPI - As for SPI, I will try to see the link but so far I have no clue !
I am too asking questions to learn. I do have a small project (a 16 relay board with 2 pots connected to ADC and 4 buttons) and am trying to design the board from scratch without the usb connection and without the usb-to-serial-ftd-chip.
Xenobius: I2C - As for as I know, this is a 2 wire protocol which can accept a maximum of 255 channels and any device connected to the same channel gets the message sent
Vincent19:
So, is that means it is better not to connect any input/output device at the MOSI, MISO and SCK pins ?
You can safely use them for push buttons and similar inputs that don't mind being driven by the programmer, and for non-critical outputs such as the Data and RS inputs of a text-mode LCD display (the LCD ignores what you put on Data and RS until you pulse EN).