14

When using a USB-to-Serial interface everything works as long as I don't go beyond 57600 Baud. At higher rates I only get giberish like this:

év.­b0JNLYÆÿ¿iëd0U²(kßÞb!
                        ú]/xscB!ï¯!BoXûÿ1ïâÖCÿ6ÌAnè*íÌC)º¿BíÞØ.C.@ÆÃwHJÂs
"YE:ñ.èFðÌCÊ÷ÞÄ
               !x
                 H
w6@BtbHJ
        ̪
          Ì6ì
H¾a¿bH.">îvy®;f<ßBÌ
               p­L¨fæH­E
­þ¼MBÞI

What makes the problem so strange is, I exchanged every component and the problem still presists. I tried different OSes (Ubuntu, Windows XP, Windows 7, Mac OS X 10.7) with 32 and 64 Bit. I tried USB-to-Serial interface from FTDI and Prolific. I tried reading the output from my Raspberry PI and from an Asterisk Appliance. I changed the cables and the wiring. Nothing helped.

I made a example with a old notebook with native COM and put the USB-to-Serial to the same connection as "sniffer" (only Rx and GND connected) to make sure the output and everything is ok as one can see on the native port. The voltage is okay. Settings for both are 115200 Baud, 8 Bit with 1 Stop and no flow control. Native is okay. USB is messed up.

I used the newest drivers and double checked all connections. I have no idea what is wrong here. As I couldn't find anyone describing problems like this I question my long experience in computer science and think I'm doing some completely wrong.

Giacomo1968
  • 58,727
Mose
  • 583

2 Answers2

6

After thinking it through and finding a single post which was a little bit in the right direction I figured out it is the only remaining possibility to invert the signal and give it a try. Fortunately FT232RL has option flags in it's EEPROM (programmable with "MProg" by FTDI) to set this:

FTDI MProg

After this, everything worked on every Baud rate. Don't ask me why, I have no technical explanation for it. I'm looking forward to get an oscilloscope for further investigation. Never saw such a strange problem before.

I tested my USB-to-Serial with a Cisco Switch too and it didn't work without this inversion.

Mose
  • 583
1

I too had the same problem connecting to our MCU at speeds over 57600 and after suspecting our UART, I found that a Silicon Labs CP2102 USB to UART Bridge (TTL) worked properly at higher baud rates without having to tweak the FTDI chipset.

Peter M
  • 11
  • 1