ME461_F11_Prelab6_10_15_11 - ME 461 Prelab #6 Fall 2011 Due...

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Unformatted text preview: ME 461 Prelab #6 Fall 2011 Due at the start of Lab #6 Suggested Reading: LSI/CSI LS7266 quadrature counter datasheet. Lab 6 manual. 1. Suppose you need to interface to a quadrature encoder attached to the shaft of a DC motor, but you do not have access to a quadrature counter chip. You decide to decode the quadrature signals with your microcontroller. You wire the A and B channel signals to two digital I/O pins and record the transitions. Assume the count starts at 0. You observe the following behavior on channels A and B. What is the count at time T? CH A CH B t = 0 t = T 2. What is meant by the statement that the LS7266 is a “dual‐axis” quadrature counter? How wide is the data bus on the LS7266? How are the registers on the LS7266 addressed? 3. How many total read/write operations are required to retrieve the 24‐bit value of one of the two counters on the LS7266? What specifically are these operations? 4. What is the filter clock prescaler? To what value should it be set to generate a 100‐kHz filter clock from the 16‐MHz SMCLK signal available from the microcontroller? What pin(s) can provide the SMCLK signal off‐chip? How are they configured to do so? 5. Write out the states (or transitions) of the D0‐D7, CS, RD, WR, X/Y, and C/D pins on the LS7266 necessary to set the X‐ and Y‐axis counter mode registers so that X4 mode is selected with normal counting. Write out the states of the above pins for resetting both counters and byte pointers. 6. Write out what you believe to be the best configurations of the CMR, IOR, and IDR registers for our application. Note that the only pins connected on the LS7266 are the ones mentioned in problem 5, the encoder inputs, and the power pins. ME 461 1 Prelab #6 7. Write the 24‐bit 2’s complement signed representation of each of the numbers below. Then, use sign extension to convert the 24‐bit numbers to their 32‐bit equivalents. Write your answers in hexadecimal. a. ‐1 b. ‐223 c. ‐19 8. With the Faulhaber motor’s gearing and its single‐pulse‐per‐rotation magnetic quadrature encoder on the input shaft, how many encoder counts will be generated with each rotation of the output shaft in X4 mode? What is the resolution in radians? 9. In quadrature X4 mode, with the motors spinning at top speed (roughly 1.5 RPS), how long will it take for the LS7266 24‐bit counter to overflow if we use a signed 24‐bit representation? ME 461 2 Prelab #6 ...
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