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Author Topic: Arduino RS232/TTL shifter programming  (Read 1021 times)
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Hi group,

i have a little problem with downloading from the IDE to optiboot (UNO) chip. Because of the nature of my project, I use the chip only (in my hardware) and a custom-made RS232/TTL converter. I added the "auto reset" circuitry, too (DTR to serial cap and a pullup of 10k).

For now, when I try to upload a sketch, I got a message "avrdude out of sync". The Pin13 led flashes correctly (3x, boot loader), when I loop back the TXD and RXD pins (at the level converter), I can "see myself" in a terminal program at the PC.

The oscilloscope shows a correct TTL serial data on TXD/RXD pins, the reset waveform at the RES pin looks good, too ...

But I can not download the binary object from IDE to chip ... When I hook up to the same wires (GND, RES, TXD, RXD) an empty Arduino UNO board and send there a compiled sketch, using the board's usbserial coverter, everything is okay.

Any idea? Thanks in forward.
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Two days of searching ... thus .. NEVER TRUST THE "PASSIVE" (couple of transistors) LEVEL CONVERTERS!

The level converter I used was something like http://www.pvelectronic.eu/hlavni-odd/podle-kategorii/rs232-ttl-uart/rs232-shifter-smd.html, see the schematics http://www.sparkfun.com/datasheets/Prototyping/RS232-Shifter-SMD.pdf. Don't trust that piece of ...  smiley-red

At lower speed, or at higher speed/low data volumes it works okay ... but for a data transfer, needed to burn a sketch thru emulated stk programmer (UNO uses 115200bps), it produces some, but only very rare, bit-errors - and you're out of sync.

A simple PL2323 board, robbed from an old mobile phone cord, fixed the problem definitely.

Solved.
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