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|17:06, 25 July 2014||Cmatteri|
When the serial port is opened there is a 32 us negative pulse on TXD (http://www.raspberrypi.org/forums/viewtopic.php?f=44&t=49867). Although many devices are error tolerant and thus not affected by this glitch, some are not and cannot easily be modified to deal with it. I would like to add a section to this page describing the glitch and how it can be avoided. It is difficult to search for information about this glitch. I did not find the linked forum post until I included 32us in the search string, and I only thought to measure the pulse because I was writing a new forum post myself. The glitch occurs when the serial port is opened, so the solution is to keep it open. This can be accomplished in bash with:
cat >/dev/ttyAMA0 &
If there are no objections I will add a small section on this glitch to this page in a few days.