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How an absolute encoder works – Binary！
Changchun Rongde Optics Co.,Ltd. Release time：2016/8/31 Browse：691it starts at the zero position for ease of explanation. In reality, the position at which any encoder would “wake up” is arbitrary. This is in fact the main benefit of an absolute encoder. If encoder power is lost, position encoder information is retained, and known instantly on power up.
At the start all of the data lines are low giving us a value of zero for each bit.
You can see by the math that we multiply the value of the data line by it’s weight, or significance
As we rotate the first 1/256th of the way around, our encoder see’s the LSB go high giving us a “one” for the first bit
Rotating another 1/256th of the way causes the first bit to fall low and the second bit to go high. Notice that as we progress through the significance of bits each bit carries twice the weight of the one before it.
Rotating another 1/256th of the way causes the first bit to fall low and the second bit to go high. Notice that as we progress through the significance of bits each bit carries twice the weight of the one before it.
We are a little over 7 degrees into our rotation and the encoders is at a count of five. Each count represents 1.40625 degrees (360 degrees/256 counts) .
In the final position of our three bit example, all bits are high giving us a value of seven. In an eight bit encoder this 0 through 7 encoders bit pattern repeats 45 times for these three bits over one rotation.
Absolute encoders are specified by the number of bits, the direction in which their count increments or decrements and the output bit pattern. Here we have covered Binary, but Absolute encoders can also output gray code.
Gray code is a binary like pattern that only allows one bit to change at a time. This makes it easier to check for errors in the count. It is a large enough topic that I will table it for discussion in a future post.
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