DC set_drive command

I read a lot of posts about set_drive command on DC.

From DC and PT User Guide I found that:

1: Drive strength is the reciprocal of the output driver resistance, and the transition time delay at an input port is the product of the drive resistance and the capacitance load of the input port.

2: By default, Design Compiler assumes zero drive resistance on input ports, meaning infinite drive strength.

3: For heavily loaded driving ports, such as clock lines, keep the drive strength setting at 0 so that Design Compiler does not buffer the net. (CLK, RESET). So, set_drive = 0

So far now pretty clear, my doubt is as follows:

If I want to specify the drive strength of my top level ports, which are driven by an external device, and I assume 50 Ohm impedance line (external driver + board trace matched), should I specify set_drive = 50 ???

I found no reference about values other than '0', in any document or posts.

Thanks in advance for your support

Yes. You should say set_drive 50 on that port. Read the Dc user guide for more info..

Dear sharath666:

Thanks for your reply.

I use set_drive 50 in my System Interface specifications but I got several max_transition violations. Then I found in DC User Guide that:

Drive strength is the reciprocal of the output driver resistance, and the transition time delay at an input port is the product of the drive resistance and the capacitance load of the input port.

And in correspondence for 50 Ohm should be set_drive 0.02 (1/50)

Do you think this is a correct drive command specification???

Best Regards

set_drive is an obsolete command.... You should set_drive_cell ....because all the calculations you to do is not worth it!!
You can look at the .lib and see the timing of an inverter and use that as the driver cell.

We usually use set_drive for top level clocks and set_driving_cell for other input ports...