downlaod sketch via serial pins

NB I have found a more appropriate section that deals with ISP, but I cannot delete this post to move it there ?

I never got a chance to buy an FTDI cable, and have always unplugged my embedded chips to tune software in an arduino board.

( I didn't add the normal ISP pins to my stock stand alone pcb that I use )

I am in a mad rush to get a project out, and thought that instead of using the SPI pins, I could just connect pins 1,2,3 , 5volts and ground from my pcb with the embedded chip ( already has bootloader ) to the pins reset, rxd and txd on the headers of my arduino board ( with no chip plugged in ).

I did a search on this but everyone seems to use the ISP pins, I generally never use the serial pins on the chip for anything else.

I made a little telemetry module last month with a USB/TTL converter ( $5 ) and it had the DTR on its header, so I stuck a cap to the reset and could rewrite the sketch no problem.

Where do you want to move this to John? Not sure if you are asking a question, or offering an implementation idea you're using for a standalone board, basically bringing out FTDI header type pins.

After I posted this in Project Guidance, I saw a section that includes ISP, but it doesn't matter now, it wont let me delete my own posts for some reason ?

Yes Bob I am suggesting it might be easier to just extend the tx and rx and reset pins from the chipless arduino to the stand alone board to save using the ISP pins. It would be exactly like running the sketch from the arduino board, but the chip is embedded in the target board.

Yes, users not allowed to delete posts, mod's got tired of loosing all our input on stuff when user decided his problem was solved and deleted the topic.

Boards like Promini bring out the Rx/Tx/DTR/VCC/GND to a header to connect FTDI Basis/equivalent to for serial downloading. I do the same on my boards.

I kept away from the traditional 6 pin header pin for ISP as it was using the SPI pins, that my early pcb bought out to other headers.

The recent telemetry project ( on the same homepage ) was the first time I used the RXD and TXD pins for anything , and as I said it was so nice to add a 100nF cap to the reset pin, and be able to work on the sketch without unplugging the chip all the time !

You never know I might abandon v22 soon and have another go at V1.04 :slight_smile:

You do seem to be confusing the ISP pins with the serial interface pins which are of course, two entirely different things and two completely different methods of programming.

In fact, they both use the reset pin - but in a different way - and either may of course (or may not) provide power.

On an Arduino board - such as the UNO, you can on the one hand, use the individual (side rows) pins instead of the ISP header if you wish, they are the same connections once you identify them.

On the other had, you can commandeer the USB to serial interface as such simply by holding the chip in reset. In the opposite direction, you can disable the USB to serial interface by holding the USB chip in reset. You really should however have half a dozen (all of $10) USB to TTL modules on hand to do this sort of thing. The only difficulty is implementing the automatic reset function. If you are doing a lot of breadboarding, a cable which implements the capacitor on RTS means you only have to identify and bring out Gnd, Txd, Rxd(, Vcc) and Reset on the board.