[SI-LIST] Impedance match

Dear all

Maybe somebody can help me a suggest me what I have to do dealing 
with the problem I desribe below:

I have to build a PCB board in which I have to interconnect a 5V TTL 
device with a 3.3V TTL one. From the 5V device goes a bus of 9 lines 
to the inputs of the 3.3V device, which is not 5V tolerant. The speed 
of the signals is 80 MHz, but the potential problem I have is with 
the rise time of the signals which I guess is about 1ns (I don`t have 
the device in my hands yet), and the bus length will probably be more 
than 7cm, so I'll have to work with the connections as they were 
transmission lines. 

How should I interconnect the devices in order to keep the integrity 
of the signal? Lets suppose that the impedance that I implement for 
the line is 50 Ohm, should I use a voltage divider in the source (ie, 
in the 5V device) or in the end? and what values for the resistors in 
order to match the impedance of the line? Or should I do someting 
completely different?

Thaks in advance



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