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I have in my BOM (Bill of materials) the following component CR21- 000-T and in the datasheet of the component : CR, CJ series is specified CR21 series as 0805 resistor.
But the 000 is specified as a chip jumper Blank = jumper chips.
Is this a resistor or a jumper?
I would expect it is a 0-ohm resistor (hence the "000"), which is often used as a jumper in all sorts of board layouts. It allows traces to be laid where they couldn't normally be laid due to another trace on the same layer.
Here is an example:
R2 is being used to jump over the trace connecting D1 to R1 (Signal 2) so that the trace between IC1 and C1 (Signal 1) doesn't have to be on another layer.
CR21-000-T is probably a mistype and should be a jumper CJ21-000-T.
In the excerpt from the datasheet you have given, you can also see that there should be a tolerance listed in the part number if it was a resistor. Because that is also missing from the number, I'd say it is just a 0805 jumper.
The exact part is also no longer available (Mouser product page), but I'd say you just can use any 0805 jumper out there as replacement.
Addition:
Based on the comments on @derstrom8 answer you were also wondering if this is a jumper like they are used on many boards to select features:
Basically: No, resistor jumpers are used like a normal resistor, so they are soldered onto the board and stay there. Commonly used to cross two signals on the same layer if other methods are not viable. For example in a single layer layout.
They can be used to select options, but typically not for an end user as it requires soldering. You can find this on some development boards though, like on the STM Nucleo (the SB refers to Solder Bridge, in the schematic they look a different to a normal jumper).
During manufacturing you can decide if you want to populate all of the resistor jumpers or not. You can use that information to, say select features or to identify a certain product if the board is used in multiple products.
I'm not exactly certain what question you are asking.
It is common practice to use a Zero-Ohm chip resistor as a jumper because it is a component that can be handled by the same machine that places all of the other similarly-sized components.
The marking on a Zero-Ohm chip jumper varies by manufacturer. I've seen many different markings: blank, a single "0", a triple zero (000), a single black rectangle with no other marking. I'm sure that there are other markings that I haven't yet seen.
It's a zero-ohm resistor, which is also a jumper.
The word 'jumper' means a piece of metal that connects two points in a circuit.
Some examples of jumpers:
