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Confusion about MSB first and LSB weight

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luckyvictor

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what does it mean by MSB first please?

e.g. If I would like to send 4095 (0000 1111 1111 1111) via SPI (8 bit per time), then should I send 0000 1111 or 1111 1111 first please?

and what does it mean by LSB has a weight of Vref/(2^23 -1) please?
 

luckyvictor,
The MSB is the Most Significant Bit. Usually this is on the left, the bit with the highest 2-to-the-x factor. So you send your sequence from the left to the right. Just like you would read it.

The LSB in your question is the Least Significant Bit, ie the smallest resolution. if you have a Vref of 10V and 2^23 = ~8.4M Then the smallest resolution of your bits is ~1.1 uV

Hope that helps.
Sckoarn
 

hi

simply the rightmost bit is LSB (least significant bit) and the left most is MSB(most significant bit).
in protocols there will be mentioned as MSB first or LSB first. i think the concept of weight comes from some sort of ADC
i assume that you are going to interface a sigma-delta adc with 24 bit out put.just refer the SPI timing diagram, you will understood whether you should send MSB or LSB first.
here the adc conversion is depends upon the reference voltage.and adc output will be full when input reaches the ref voltage level the weight of LSB means the minimum input change required to produce one bit change in LSB


ml
 

thanks for all your reply, so to send 4096, I will first send out 0000 1111, then send 1111 1111, and the weight of LSB is simply just the minimum resolution, a voltage correspond to one bit
 

Yes, you will send it bit by bit starting from left to right.
 

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