Arduino Programmer (FTDI) Questions

I am currently making a board that has both an Arduino and a Parallax Propeller. When working with Arduino I usually use a standard serial port adapter for programming, but when working with a Prop I use one of these

http://www.parallax.com/Store/Microcontrollers/PropellerTools/tabid/143/ProductID/398/List/1/Default.aspx?SortField=ProductName,ProductName

It is basically an FTDI that has a circuit to pull DTR low, which is the Propellers reset line. On the product page it says compatible with 3.3v and 5v micros. Basically on my board it would be nice to use a switch to select which chip I want to program, but have only one programming plug for both Arduino and Propeller, which accepts a Prop Plug.

I tried tying the prop plug Tx>RX, Rx>TX, VSS>GRND, RES>RES, to my Arduino. When I tried to upload a sketch I got an out of sync error. Im assuming this has something to do with the reset line. I was thinking Arduino may use CTS instead of DTR for reset, im not sure but there are no options I can find in the Arduino IDE to change the reset Pin. Is it possible to use DTR as the reset line? I would really like to get this prop plug programming an Arduino!

That should work if you place a 0.1uF cap in series with the DTR pin, and have a 10K pullup between Reset and +5V (on the "other" side, the chip side).

Like this:

Oh ok thank you very much, Im about to walk out the door right now, but I will try this out when I get home.

So the Arduino IDE uses DTR to send the reset signal? I had thought it used CTS, that makes life easier. The only other issue as I stated earlier is the DTR signal is not directly broken out it passes through a few transistors to invert the signal, this is becuase the propeller expects the RES signal to stay hi and to reset it gets pulled low. I know this circuit is not on those FTDI break out boards most people buy, on the other hand it looks to me like the Arduiono may work the same way and that is its reasoning for the 10k pull up? But why a cap in series?

On my FTDI cable (as shown above) it brings RTS low, and there is no DTR.

But why a cap in series?

RTS stays low which would keep the chip in reset. The cap recharges from the 10K resistor and lets the processor leave reset.

Hi Nick

From your other diagrams I've always left CTS without connection but in this one you've got it bridged with GND. I don't think I've had any issues - but is there a benefit I'd be missing by leaving it disconnected or floating?

Cheers ! Geoff

I initially had it disconnected, so I doubt you will have issues. I think CTS is an outwards signal so it only really affects the sending end.

http://en.wikipedia.org/wiki/RS-232_RTS/CTS#RTS.2FCTS_handshaking

The DTE asserts RTS to indicate a desire to transmit to the DCE, and the DCE asserts CTS in response to grant permission.

So really it is grounded to assert that it is OK to send, rather than left floating, however I think it is probably ignored.

Interesting. Sounds like grounding it is a good idea though. Will do that ongoing.

Thanks