1. Home
  2. Field-Programmable Gate Arrays
  3. Phase detector for DLL

Phase detector for DLL

Hi ,

I am new programmer in VHDL and i have to realize a DLL in an ACTEL ProASIC board.

I am using Libero 4.6 and Model Sim 5.6b.

I have decided to use as example the 74HC297.

I am having problems to implement a Edge Controlled phase detector using a simple SRlatch!(not a doubble SRlatch!)

CAn anyone tell me why I got this message on ModelSim: "Iteration limit reached. Possible zero delay oscillation. See the manual."

Is not possible to instatiate a simple Latch on Fpga?

I am sure to instante a latch because I have veruified on the netlist in Synplify! and on the Designer netlist a Dlatch has been implemented!

Is it only a problem in the use of a Simulator?

Furthermore I am trying to simulate a simple Dlatch with asyncronous clear with the following testbench:

1) D imput line a signal that represent the frequency I want to lock. 2) Clear input a signal that is opposite to D that represent the frequency that come from the DCO(to "simulate" a phase detector in the case when I am in Lock state )

Thanks for any help! and tips you can suggest!

Massimo

Reply to
Massi
Loading thread data ...

Perhaps you can post your code in the appropriate forum: comp.lang.vhdl.

Reply to
Andy Peters

I think it is a problem with sensitivity lists. At least that's where I have seen this error. What happens is that the you have listet one of a process' output signals in the sensitivity list, so that when the process runs, it causes itself to run again. In theory this causes an infinete loop, but the simulator protects you against this by having an iteration limit.

Try this:

process(clk, reset) begin if (reset = '0') then d_out in Synplify! and on the Designer netlist a Dlatch has been

It may be, but it sort of sounds like you are doing something like implementing the latch with and gates and stuff, like you would in a schematic program, at the most basic level. This is not the best way to do it.

-- Anders

Reply to
Anders Hellerup Madsen

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.