why don't Proasic3/E library have D flip flop with preset primitive?

[Sumathigokul]

Hi All...

I know that Microsemi-ProAsic3/E has D latch with preset input, but it do not have D flipflop with preset option....

Do anyone know any valid reason for that???

Thank you.

 

[FvM]

Because they decided to make the logic core as they did.

Having FFs with reset only (which can be used as preset only by inverting the logic) is a tendency also with other FPGA vendors, e.g. Altera. They abandoned full FF functionality with Cyclone/Stratix II, a kind of trade-off.

The bad thing is that FF's with asynchronous load input or both clear/preset can be only implemented as an unhandy and slow emulation circuit. But the function is mostly unwanted in synchronous FPGA design anyway.