AVR-Chat

I am working with linx txd-433-kh RF module for remote communications.  I am 
using Atmel atmega8515 microcontroller w/a SDK500 board.  The problem I am 
having is that the when I take the data pins high on the tx module it is 
being passed a voltage of around 5.80v.  The tx module wants the voltage 
below 5 to function so I attempted to place a 180ohm resistor in series 
which didnt do anything to the voltage but if I parallel the resistor with 
ground I get acceptable voltage and the module works.  Thing is for 1 that 
means I will have to run resistors on all the TX data pins coming from the 
microcontroller.  This also creates heat on the resistors ( I guess this is 
acceptable ) and causes power loss which may be a factor running from 
batteries.

Is their another better way around this?  BTW dropping the voltage to the 
microcontroller from the battery is not currently an option.