Go Down

Topic: Programming an UNO clone using a FTDI cable (Read 2986 times) previous topic - next topic

#15
Jan 16, 2013, 12:44 am Last Edit: Jan 16, 2013, 12:53 am by danomahoney Reason: 1
That's interesting Westfw,

I didn't mention it but while I was waiting for the breakout board to arrive I hacked an UNO board with the 328 removed, soldered a wire to the auto reset cap (because I wanted to test the clone circuit as much as possible), connected this and GND, TX, RX to a 6 way leaded socket (pin-out as per FTDI cable, CTS tied to GND and 5V not necessary as clone has own) and was able to program with 100% success. The clone board has a 16MHz crystal with 2 x 22pF caps, auto reset cap 100nF. The supply rails are clean with plenty of decoupling.

When I've got time I will make some measurements with a 'scope and post the findings.

ATB Dan

oric_dan


The 115200bps serial rate used by optiboot is not particularly accurate on a 16MHz AVR.  If (say)
neither the AVR nor the FTDI had a crystal-controlled clock ...


I can imagine this problem would get worse at higher baud rates. Why on earth do they
put a 5% tolerance ceramic resonator in the UNO along with using optiboot at 115200?

westfw

Quote
a 5% tolerance ceramic resonator
That's extremely unlikely.  I couldn't even find any 5% resonators.  (I *did* find a bunch of 0.5% resonators (which is more typical) whose "short descriptions" were missing the decimal points, so it LOOKED like they might be 5%.  But they weren't.)

oric_dan

Oops, misfire, it is 0.5%, not 5%. Still many times worse than 20-50 PPM for crystals, which
is 0.002-0.005% [if in error again, well, maths isn't strong in the mornings].

Go Up
 


Please enter a valid email to subscribe

Confirm your email address

We need to confirm your email address.
To complete the subscription, please click the link in the email we just sent you.

Thank you for subscribing!

Arduino
via Egeo 16
Torino, 10131
Italy