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Newbie siva1234
Newbie
4,089 Views
Registered: ‎08-13-2017

Need help in logic cpmbatible

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HI ,
I am use "XC6SLX45-2CSG484C" spartan 6 FPGA interface with  PIC32MX110F016B-I/SO(Uart Communication). need to perfom logic compatible with microcontroller(  PIC32MX110F016B-I/SO is transmitter)

because if sinking current goes high the logic combatable will fail with microcontroller .
Data sheet of microcontroller (http://ww1.microchip.com/downloads/en/DeviceDoc/61168D.pdf) in page 251 the values of Voh Values of the PIC is given. From that when the drive current (microcontroller is transmitter) is above 12mA the logic compatible will fail .

So want to know the max sink current of Fpga in Uart communications . hope it's less then 10mA . Please clarify

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Scholar embedded
Scholar
7,286 Views
Registered: ‎06-09-2011

Re: Need help in logic cpmbatible

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@siva1234,

When you configure an IO as input, a CMOS transistor - assuming your IOSTANDARD is LVCMOS33 - would be connected to the pad!. So, it would draw a CMOS transistor gate leakage current from Driver - which is in your case the transmitter pin of PIC controller. This value is a very low current that every transmitter can supply - according to the page 5 of ds162.pdf - it. See below from datasheet:

Leakage.jpg

I should add that DRIVE Strength is applicable to Output pins, not input pin.

So, You do not need to worry about your PIC pin if it can afford leakage current of FPGA pin or not!.

 

Hope this will help,

Hossein

View solution in original post

8 Replies
Scholar u4223374
Scholar
4,079 Views
Registered: ‎04-26-2015

Re: Need help in logic cpmbatible

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The source/sink current should be very close to zero (microamps). The maximum source/sink currents are irrelevant because you won't be anywhere near those limits.

Newbie siva1234
Newbie
4,068 Views
Registered: ‎08-13-2017

Re: Need help in logic cpmbatible

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Hi

 

Thank you for reply,

 

It's applicable for all Interface or UART Alone ??? Because in datasheet(FPGA) nowhere value is given(Iil,Iih or Sink current)

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Voyager
Voyager
4,058 Views
Registered: ‎06-24-2013

Re: Need help in logic cpmbatible

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Hey @siva1234,

 

On Spartan 6 you can control the output drive strength on a per pin basis (with the DRIVE attribute) roughly between 2mA and 24mA depending on the I/O Standard. LVCMOS12 only supports the 2, 4, 6, 8, and 12 mA DRIVE settings. LVCMOS15 only supports the 2, 4, 6, 8, 12, and 16 mA DRIVE settings.

 

You can find the details in UG381.

 

Hope this helps,

Herbert

-------------- Yes, I do this for fun!
Newbie siva1234
Newbie
4,054 Views
Registered: ‎08-13-2017

Re: Need help in logic cpmbatible

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Hi Herbert,
We can control the output drive strength of FPGA. But I want to know the input value(Sink current) . When Pic is tx and Fpga is receiver the input current (sinking current ) (Iil.Iih) that's my need.
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Scholar embedded
Scholar
7,287 Views
Registered: ‎06-09-2011

Re: Need help in logic cpmbatible

Jump to solution

@siva1234,

When you configure an IO as input, a CMOS transistor - assuming your IOSTANDARD is LVCMOS33 - would be connected to the pad!. So, it would draw a CMOS transistor gate leakage current from Driver - which is in your case the transmitter pin of PIC controller. This value is a very low current that every transmitter can supply - according to the page 5 of ds162.pdf - it. See below from datasheet:

Leakage.jpg

I should add that DRIVE Strength is applicable to Output pins, not input pin.

So, You do not need to worry about your PIC pin if it can afford leakage current of FPGA pin or not!.

 

Hope this will help,

Hossein

View solution in original post

Voyager
Voyager
4,040 Views
Registered: ‎06-24-2013

Re: Need help in logic cpmbatible

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@siva1234,

 

I want to know the input value(Sink current).

When Pic is tx and Fpga is receiver the input current (sinking current ) (Iil.Iih) that's my need.

Ah, sorry, that was't obvious to me.

 

That would be the Input Leakage current (± 15uA), which you can find in DS162, if you are inside the allowed input voltage range for the FPGA pin and do not have any on chip termination enabled.

 

Hope this helps,

Herbert

-------------- Yes, I do this for fun!
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Newbie siva1234
Newbie
4,036 Views
Registered: ‎08-13-2017

Re: Need help in logic cpmbatible

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Thank you guys !!

 

Now I understand ... :-)

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Voyager
Voyager
4,033 Views
Registered: ‎06-24-2013

Re: Need help in logic cpmbatible

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You're welcome!

 

All the best,

Herbert

-------------- Yes, I do this for fun!
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