5v TTL to/from LVTTL

There are several solutions;

1) If your signals are unidirectional, or are bidirectional, but you have a direction control bit, then you can use 5V tolerant buffers; these devices are powered from 3.3V, but can handle 5V on their pins.

If the 5V devices you are communicating are TTL compatible, then these 3.3V translators can work fine.

You need to check the VIH and VIL limits of the 5V logic are met by the buffer.

If you only have a few I/O lines, then look at the TinyLogic devices from Fairchild, and TI (TinyLogic is the Fairchild name). Look in a translator guide and you'll find examples of 8-bit, 16-bit, etc devices.

2) If you have to attach a 3.3V device to a bidirectional bus, and you do not know which direction the signals on the bus are going to be, then you can protect your 3.3V logic using a bus switch. The bus switch will pass the traffic on the 5V bus through itself, and clamp the highs to below 3.3V.

So what is it you need?

Cheers,

Dave