Hi - I have bought a chinese Altera dev kit: The fpga i/o is interfaced to an lcd panel using 'level shift' interface chip. BUT the levels on both sides of this chip are the same!I've noticed this quite often on various fpga schematics - why is this chip needed if the levels are the same? Just for info : the bus to the lcd panel is bidirectional on my board - but I can't see why the level-shift buffer is needed at all. I've even seen some schematics where the lcd panel is only written to (ie uni-directional), and the levels are identical - why is this chip needed? Thanks John B.
I don't have your board schematics, nor I know what type of interface is used there, so I only can make some guesses.There are more reasons for which the designer may want to add a 'level shift' inferface, besides actually shifting voltage levels. First of all it could serve as a buffer, in order to drive a current higher that that provided by fpga I/Os. Or it could be used to somehow protect FPGA ports against damage, in the case the LCD comes as a plug-in component, and/or if the same LCD signals are available as general purpose user I/Os (it's easier and cheaper to replace a small buffer chip than the FPGA).
Many thanks for your reply - you must be right - it must be for buffering and/or protection reasons. (the LCD is a plug in module). Thanks for the comprehensive response. John B.