Hi,I am designing cyclone 3 FPGA board in which i have come across cmos logic circuit and ttl logic circuit. can i connect 3.3v of both the cmos and ttl logic? what are all the things we have to taken care when go for different logics? Thanx in advance :) Regards, Shahul
A 3.3V I/O standard can drive LVTTL, LVCMOS(both 3.3V supply) and TTL (5V supply). To drive 5V CMOS (e.g. 74HC family), you need a level converter. 74HCT logic has TTL levels on input and can be driven by the 3.3V I/O.5V logic must not drive the FPGA without level conversion or voltage clamping.