Need help in schematic design (IMPORTANT)

[Altera_Forum]

Hi, 

I am designing cyclone3 FPGA board.In which it has ADV7123 intefacing. i am planning to MUX some of the basic peripherals such us led, seven segment display with data pin of ADV7123. example: RED0 - RED9 is muxed with LED0 - LED9 GREEN0 - GREEN9 is muxed WITH SEVENS EGMENT DATA PIN.  Is it possible to do so?  i have attached datasheet of ADV7123. Its basic interfacing connection is shown in page 20.  Thanx in advance  Regards, shahul;)

[Altera_Forum]

Leds and 7seg displays are controlled through std LVTTL signals which is what ADV7123 needs, so the answers is, generally talking, yes. 

On the practical side, if you keep on driving leds and display with those signals, you must account for current drawn by them and for extra capacitive loading. This could affect the performance if you are planning to drive the signals at high frequencies.  Regards Cris

[Altera_Forum]

Hi cris, 

Thank u for prompt replay.    --- Quote Start ---   This could affect the performance if you are planning to drive the signals at high frequencies.  --- Quote End ---    regarding current no problem.but i don't understand signals at high frequency. Did u specify about the input crystal oscillator frequency.  Regards, shahul:)

[Altera_Forum]

I mean the effect of extra load on the signal could lead to slower step response, especially if you have a load which sinks much more current than a logic port, like a LED does. Besides, longer or branched traces can lead to signal overshoot or ringing. 

Those are usually not a great problem if you work at low frequencies, up to a few MHz but you must pay attention if you plan to drive the interface in the tens of MHz range. Please note that I don't know how are you going to connect the ADV7123 device. I assumed you DO actually have leds and 7seg display connected in parallel to the interface signals. Maybe I missed the point and you are simply keeping the original signal names but no led is anymore there.  Cris