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strange UART junk characters

Question asked by ROB LUND on Sep 30, 2010
Latest reply on Oct 6, 2010 by bigmac

Hey all, I'm troubleshooting an odd problem.  I have a DEMO9S08QG8 board, on which I've programmed the SCI for UART functions.  The demo board has an RS232 transceiver.  I'm using Realterm to talk to this board.  That's all working fine, except for a few stray "junk" characters that my serial port is receiving from the ether.

 

See the screenshot for my Realterm app interface.  A simple EEPROM controller.  Right under the "Enter memory address", I've entered a "23".  Notice the block between the 2 and 3?  This appears to be some other ASCII escape code, perhaps a 0xDF or 0xFE.  Similar thing after the line "Enter data".

 

Also, notice that the CTS and DCD and DSR lights are on.  The demo board seems to have RTS and CTS wired for hardware flow control (see schematic screenshot).  I have attempted the "None" option as well as other hardware flow control options in Realterm.  None seem to quiet the junk.

 

On a whime, I loaded this firmware into a different MC9S08QG8 target board, which has an RX/TX only transceiver.  I see none of these junk characters.

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