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Topic: ArduinoISP on Uno requires 10uF cap -- WHY? (Read 4 times) previous topic - next topic

SirNickity

I'm really glad someone brought this up.  I hate doing things and not understanding why.  Thanks everyone for the thorough explanations.

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My view is that the USB to serial AVR chip code should be tweaked to use RTS rather than DTR.


Six-pin FTDI cables don't have RTS pins.  Just DTR (and CTS).

bperrybap


I'm really glad someone brought this up.  I hate doing things and not understanding why.  Thanks everyone for the thorough explanations.

Quote
My view is that the USB to serial AVR chip code should be tweaked to use RTS rather than DTR.


Six-pin FTDI cables don't have RTS pins.  Just DTR (and CTS).



Ummm.... Go have a another look at the FTDI 6 pin connector pinout.
Here is a link to the data sheet. See pages 17 and 19.
http://www.ftdichip.com/Support/Documents/DataSheets/Cables/DS_TTL-232R_CABLES.pdf
DTR is not on the 6 pin cable. It uses RTS instead.
Even the label on the Arduino Pro board labeled it correctly as RTS with respect to a standard 6 pin
FTDI cable.
http://arduino.cc/it/Main/ArduinoBoardPro




But all this is irrelevant with respect to the code inside the 8u/16u AVR chip that has replaced the FTDI chip
for the USB to serial conversion.
To switch to using RTS instead of DTR is a simple code change inside the 8u/16u AVR chip to use the RTS status bit in the messages
vs the DTR bit when driving the output that goes to the other AVR reset pin.


--- bill

SirNickity


westfw

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USB to serial AVR chip code should be tweaked to use RTS

If we're going to fiddle with the 8u2 and "arduino" programmer type in avrdude, I'd like to get away from using rs232 signals at all.  I think PaulS suggested picking a rare and uncommon bitrate, and resetting the Arduino AVR when that was set.

OTOH, "backward compatibility with 500,000 existing Arduinos..."

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what is it about UNO in particular?

Different and Dumber bootloader, running at a different bitrate.  Possibly a newer version of Avrdude in newer IDE releases.
Prior to Uno, the Bootloader would exit quickly when it saw "illegal" commands.  The Uno bootloader isn't smart enough to check for illegal commands (although the most recent version can check for improperly received commands, as "probably" occur when commands are received at the wrong speed.)

kf2qd

Another reason is that there have been attempts to reduce the size of the bootloader. The smaller it is, the less bells and whistles. Could add all kinds of capabilities to it, but that would just lead to complaints doe to the amount of memory that it would use.

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