high input to CPLD

Hi Friends,

I am working on project, where I am using CPLD operating at 5V supply.
Can we direcly give the high inut voltage i.e. +5V to its input pin?
Or we have to connect a resistor in between them?
If so then how to select a value for +5V supply.
simillarly give information for grounding the i/o pin.

Regards,
Sonali

> I am working on project, where I am using CPLD operating at 5V supply.
> Can we direcly give the high inut voltage i.e. +5V to its input pin?

that depends on the chip you use ...
usually they support 1-2 higher voltage standards as input than they 
deliver as output but you can only find out about that by looking to the 
data-sheet of *your* CPLD ...


the newer parts run on lower voltage and at least recent FPGAs would not 
even support 5V - that is why we use some of the old FPGAs as well ...
Looks like you can still buy them but recent Xilinx ISE tools do not 
support them any more so we have a few machines still running ISE 4!


bye,
Michael

VCC given to IC is +5V.
so then can i directly give +5V to CPLD XC9536's logic pin which
configured as input.
Inside there is a multiplexer.
it has one control signal.
how to give '1' i.e. logic high input to CPLD.
Should I need to connect resistor in between VCC and that pin.
What should be its value taking account of power dessipation.

Pradnya.

VCC given to IC is +5V.
so then can i directly give +5V to CPLD XC9536's logic pin which
configured as input.
Inside there is a multiplexer.
it has one control signal.
how to give '1' i.e. logic high input to CPLD.
Should I need to connect resistor in between VCC and that pin.
What should be its value taking account of power dessipation.

Pradnya.

Pradnya, you must learn to read a data sheet.
For 9536 it says:
recommended Operating Conditions
VIH High Level Input Voltage max Vccint + 0.5 V
where Vccint = 4.75 to 5.25 V.

That tells you that you can connect the input to Vccint.
If you like to put a resistor in series, that resistor does not add to
the power consumption.
Peter Alfke

You should probably connect it through a pull-up resistor for safety.
What happens if you accidentally drive that pin to '0'?  You would blow
up the output transistor!  Of course if you say that it is an input pin
then it shouldn't matter, but it's still safer to go through a
resistor.

Just make sure you choose the resistor value according to how much
current that pin can handle.


Cheers
Ernie