What are Pull ups?

R

rider

Guest
Hi!

I am using SPARTAN 2 XC2S150 for my design. I have a question
regarding pull up resistors. I am using ISE5.1.

1)What is meant by optional pull ups? There are options in the
Constraints Editor to insert pull ups at the I/Os. Are these PERMANENT
pull ups or just during configuration? If I select these pull ups,
then i also need to set M2M1M0=100 ?

2)Alternatively if i DO NOT select those pull ups in the Constraints
editor, but i still set M2M1M0=100 then what will happen? Pull ups
will be used for configuration only?

3) Do i need to connect all my VCCO pins to 3.3V and VCCINT to 2.5V?
All GND pins on the pacakge be grounded?

4)If I use one clock signal in my design, then it can be input on only
one IGCKO(input global clock buffer) or i need to connect all IGCK's
to this clk signal?

Regards
Rider
 
rider wrote:

Hi!

I am using SPARTAN 2 XC2S150 for my design. I have a question
regarding pull up resistors. I am using ISE5.1.

1)What is meant by optional pull ups? There are options in the
Constraints Editor to insert pull ups at the I/Os. Are these PERMANENT
pull ups or just during configuration? If I select these pull ups,
then i also need to set M2M1M0=100 ?
Well, they're only permanent from the standpoint that they are there
after the device is configured.

You do not need M[2..0] set to 100 to get these pullups. They are in the
device configuration. If you set M[2..0] to be 100 you will also get
these pullups at power up and during configuration. If you set M[2..0]
to 000, then the pins will be three-state (hi-z) at power up and during
configuration.

2)Alternatively if i DO NOT select those pull ups in the Constraints
editor, but i still set M2M1M0=100 then what will happen? Pull ups
will be used for configuration only?
See previous answer.

3) Do i need to connect all my VCCO pins to 3.3V and VCCINT to 2.5V?
All GND pins on the pacakge be grounded?
Yes, yes, and yes.

4)If I use one clock signal in my design, then it can be input on only
one IGCKO(input global clock buffer) or i need to connect all IGCK's
to this clk signal?
You should input this on a single global clock. If you input this on
multiple clocks, even if you use a DLL, you may introduce additional
skew between the clocks.

Regards
Rider
 
Rider,

See inline.

Regards, Wei
1)What is meant by optional pull ups? There are options in the
Constraints Editor to insert pull ups at the I/Os. Are these PERMANENT
pull ups or just during configuration? If I select these pull ups,
then i also need to set M2M1M0=100 ?
The pullup that you set in constraints editor is a post-config setting only.
http://toolbox.xilinx.com/docsan/xilinx6/books/data/docs/lib/lib0338_306.html
2)Alternatively if i DO NOT select those pull ups in the Constraints
editor, but i still set M2M1M0=100 then what will happen? Pull ups
will be used for configuration only?
See above
3) Do i need to connect all my VCCO pins to 3.3V and VCCINT to 2.5V?
All GND pins on the pacakge be grounded?
Solution 17240
http://support.xilinx.com/xlnx/xil_ans_display.jsp?iLanguageID=1&iCountryID=1&getPagePath=17240
4)If I use one clock signal in my design, then it can be input on only
one IGCKO(input global clock buffer) or i need to connect all IGCK's
to this clk signal?
As long as clock region rule is not violated. Check datasheet for more
info.
http://support.xilinx.com/xlnx/xil_ans_display.jsp?iLanguageID=1&iCountryID=1&getPagePath=172401
Regards
Rider
 

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