Programmable Devices
CPLDs, FPGAs, SoC FPGAs, Configuration, and Transceivers
21602 Обсуждение

trying to constrain external clock driver (TQ), searching help

Altera_Forum
Почетный участник II
1 358Просмотр.

Hello, 

 

as the title already reveals, I am trying to constrain my external hardware in the TimeQuest. After my "sysclk_out" in in my design there is a clock driver on my board, that I would like to constrain. 

 

It is a CDCVF2505PW, the datasheet can be found at the ti website: http://focus.ti.com/lit/ds/symlink/cdcvf2505.pdf 

 

I have added a sketch of the system to this thread that shows the path I want to constrain. Unfortunately, I did not know how to calculate or read Tsu/Th from the datasheet. 

 

Can someone with some experience explain or give me the solution to constrain this path, please. 

 

Thanks, Peter.
0 баллов
3 Ответы
Altera_Forum
Почетный участник II
581Просмотр.

I don't think there is a Tsu/Th to a clock divider. Tsu/Th are concepts of data related to a clock, where this is "just a clock". In general you don't constrain this.

Altera_Forum
Почетный участник II
581Просмотр.

The CDCVF2505PW is a PLL-based clock driver, as such it adds no delay to your clock output signal and you don't have to take any provision for it. You can see it as a virtual device which adds zero delay.

Altera_Forum
Почетный участник II
581Просмотр.

Thanks, for your replies. I was unsure about this, because to my external sdram I have got this clock driver in the clock circuit path on my circuit board, but there is no component in my data circuit path. So I expected, that I must tell the TimeQuest in any way, that the path in relation is delayed. If you now say, that there is no added delay for the clock output, I will just ignore the driver and not constrain the path. 

 

Thanks.
Ответить