I just bought the LS20031 gps unit and I bought a logic level shifter as it is 3.3v, but after reading the spec sheet, it appears to use “TTL level” serial interface. So, my question is, if I hook it up to the serial pins on my Atmega32 running at 5v, will it be OK? I know I have to supply 3.3v to the gps unit for power, but it would be simpler to directly connect the UART pins of the AVR directly to the gps without the level shifter, I just don’t want to take a chance of blowing the gps when I send commands over the serial line.
No.
Page 10, section 8 of the [datasheet has all the details… 
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