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[Reply #15 on:]

True, but then you have to make sure you don't have anything connected to Tx/Rx for best results.

So, is that means it is better not to connect any input/output device at the MOSI, MISO and SCK pins ?

It depends on the device a bit. SPI devices are designed for this sort of thing, you just don't activate them through their slave select pin.

So do this means that I cant connect anything to this 2 pins ? Or it is not adisable to connect anything here?

[Reply #16 on:]

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.

[Reply #17 on:]

You mention it has pull ups. So meaning that I can put a button there as an input ?

Correct me if I am wrong

[Reply #18 on:]

A button to ground should work. Are these just a lot of hypothetical questions or do we have a project here?

[Reply #19 on:]

Yea, a button to GND and to TX/RX pins should just make it a pull up button right ? So, I think I no need this below code to activate the pull up ?

Code:

digitalWrite(0/1, HIGH)

I am just asking for my own notes so I will becareful when in my project

[Reply #20 on:]

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.

[Reply #21 on:]

Thanks alot !

[Reply #22 on:]

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 !

Cheers

[Reply #23 on:]

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.

[Reply #24 on:]

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

No. Better read this:

http://www.gammon.com.au/i2c
http://www.gammon.com.au/spi

http://www.gammon.com.au/forum/?id=10918

[Reply #25 on:]

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).