What's the purpose of R20 in this schematic

  • Thread starter j777
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In summary, The purpose of R20 in the schematic is to provide the user with the option of using either common or separate offboard clocks. On the other hand, R35 allows for offboard selection of one of two clocks and also serves as protection for the offboard clock drivers in case both are erroneously connected. The presence of a zero Ohm resistor as a jumper in some packages allows for the use of a real part as a test point or for separate testing of the two clocks. In the second schematic, R35 serves a similar function as R20, but with a different resistance value.
  • #1
j777
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I'm studying a portion of a schematic from an evaluation board. What's the purpose of R20 in the attached schematic?
 

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  • #2
Isn't it just a connection between the two clocks?
It's common to draw a link as a zero Ohm resistor in some packages, it let's the layout software actualy put a real part there so you can use it as a test point, or remove it to test the two clocks separately. On surface mount it's the normal way to do a link.
 
  • #3
ja, it's a jumper
 
  • #4
I'm not so sure that it's just a jumper...

Here's a snippet from a similar eval board. In this schematic the resistor is R35. Any ideas?

The full schematic for this snippet can be viewed is at http://www.olimex.com/dev/images/ARM/ATMEL/SAM9-L9260-REV-B-sch.gif"
 

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  • #5
Hard to say. 100 Ohms is different from the zero Ohm jumper in your first post. 100 Ohms is more like a termination, but zero Ohms is almost always a jumper for stuff options.
 
  • #6
Thanks for all the input.

I still don't know what the 100 Ohm resistor is for but my theory for the zero Ohm resistor is that it gives the user the option of accessing the SD card via SPI or SDIO. Does that make sense?
 
  • #7
R20 allows the user to use either common or separate offboard clocks.

R35 allows offboard selection of one of two clocks. If you happen to erroniously connect both, the 100 ohms will protect the offboard clock drivers.
 

Related to What's the purpose of R20 in this schematic

What is R20 in this schematic?

R20 is a resistor component in an electrical circuit. It is represented by the letter "R" followed by a number that identifies its specific location in the schematic.

What is the purpose of R20 in this schematic?

The purpose of R20 is to limit and control the flow of electric current in the circuit. Its value, measured in ohms, determines the amount of resistance it provides.

Why is R20 necessary in this schematic?

R20 is necessary in this schematic because it helps to ensure that the electrical components in the circuit are not overloaded with too much current. It also helps to maintain the stability and functionality of the circuit.

Can R20 be replaced with a different component?

Yes, R20 can be replaced with a different component as long as it has the same resistance value. However, changing the resistance value may affect the overall function of the circuit and should be done with caution.

How do I determine the appropriate resistance value for R20?

The appropriate resistance value for R20 depends on the specific requirements of the circuit. It can be calculated using Ohm's Law, or it may be specified in the schematic or circuit design documentation.

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