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How to use internal DLL or DCM of FPGA spartan2

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shreshtha

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fpga dcm

i have read the data sheet but still i dont know how to instantiate the DCM
please tell the "code"

can it be used for multiplication and division both?

what's the advantage of using it instead of creation our own clk divider ...

is it ised for multirate system and their synchronization?

please help.

i ll be very thank ful 2 u;
 

dcm fpga

You can find instantiation template in the xilinx library guide. Read also XAPP174.
There are two primitives in spartan2 CLKDLL and CLKDLLHF. With the CLKDLL you can perform multiplication by 2 and division by 1.5, 2, 2.5, 3, 4, 5, 8 and 16, input up to 100MHz for -6 version. CLKDLLHF will run up to 200MHz, but you cannot make multiplication with it. Using the divider from DLL will spare some logic, this would be one advantage. If you want to use the DLL with a source other than a BUFG or IBUFG, just make sure you put this into environment variables: XIL_MAP_ALLOW_ANY_DLL_INPUT=TRUE
DCM is a primitive only in spartan 3 and virtex II series, not in Spartan 2.

/pisoiu
 

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    shreshtha

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dcm in fpga

hi,
dcm and dlls are used for both division and multiplication of frequency.

with regards,
kul.
 

how to use dcm

hi shreshtha,
u can easily insert DCM models inside your design.
ISE has got the templates for instantiating all the primitives. just have a look at ISEtemplate->VHDL->DevicePrimitiveInstantiation->FPGA->Clock Components->DCM.
 

clkdll spartan 2

you can direct instantiate DLL in your code, same as you do for ram.

shreshtha said:
i have read the data sheet but still i dont know how to instantiate the DCM
please tell the "code"

can it be used for multiplication and division both?

what's the advantage of using it instead of creation our own clk divider ...

is it ised for multirate system and their synchronization?

please help.

i ll be very thank ful 2 u;
Click to expand...
 

spartan 2 dll

shreshtha said:
i have read the data sheet but still i dont know how to instantiate the DCM
please tell the "code"
Click to expand...
Look in the User Guide, not the Data Sheet.

If all you need to do is divide a clock frequency by some integer value, then don't bother using a DCM. Just use a counter. However, if you need the output to be phase-aligned with the input clock, or offset by a specified (or adjustable) phase angle, or if your input/output frequency ratio is not an integer, then a counter probably won't suffice, so it's time to try a DCM.
 

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