That does not need to be a problem. If the logic is TTL compatible then the thresholds are well within the range of logic operating from 3.3V. TTL specifies that anything above 1.4V is regarded '1' and eveything below 0.7V is '0'.
As far as I'm aware, there is no overarching specification for TTL logic level, just de facto standards steered by major manufacturers.
More clearly, a typical 3.3V LVTTL device producing V
OLmax=0.4V / V
OHmin=2.4V should theoretically have no problem interfacing with a typical 5V TTL device accepting V
ILmax=0.8V / V
IHmin=2.0V.
Some design considerations:
* Including a 3.3V device in a 5V circuit means an additional regulator to supply the power rail. Depending on device power requirements, this can be as simple as an additional resistor and 3.3V Zener diode with decoupling caps, to a complicated 3.3V switching regulator.
* Care must be taken when driving 5V signals into a 3.3V device. Selecting a 3.3V device with 5V-tolerant inputs will reduce complexity, but will also have a negative impact on reliability, which may or may not be important to you depending on application.
* Pay close attention to your device's current drive spec. This will play an important role in designing sound termination strategy.
EDIT: Forgot subscripting.