Are you sure the serial port settings are the same on both ends?
Usually, if you have a level translation issue, you should see nothing
at all. If the levels are correct, but the baud rate, or stop bit
settings don't match, you can see garbage show up. I would suggest
using Minicom and a regular Linux box (or Windows and Hyperterminal)
to verify that the port settings are OK before you proceed further. If
you have access to a scope, use it to measure the bit rate and see
that it matches the settings you expect.
-Jim
On Sat, Mar 21, 2009 at 8:38 PM, Jason Stahls <> wrote:
> teohoeeng wrote:
>> I use 74LVC245AN (a level shifter), suppose similar as 74LVC3245. However,
>> today I make all the connection between my 5V TTL sensor to 3.3V TTL TS7800
>> serial port using this level shifter, I got the same garbage data problem.
>> Seems strange that this problem doesn't go away...seem that I am trying to
>> solve multiple problems or one unknown problem.
>>
>> Don't anyone has manage to get a 5V TTL sensor to work with 3.3V TTL
>> serial port on TS7800. I tested my 3.3V TTL GPS sensor working with the
>> TS7800 5V TTL serial port though with the same C code. So I rule out any
>> software problem.
>>
>> Anyone know if there is a need to place an inverter before the level
>> shifter to invert the signal between 3.3V TTL and 5V TTL, like the inversion
>> done in RS232 standards from TTL?
>
> Why not use some transistors? There's gotta be about 50 ways to do it
> :) Basically, setup one transistor to invert, and the second is for
> level shift.
>
> Jason
>
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