AN2364 Freescale Semiconductor / Motorola, AN2364 Datasheet - Page 24

• Manufacturer Part Number: AN2364
• Description: Using the Table Stepper Motor TPU Function (TSM) with the MPC500 Family
• Manufacturer: Freescale Semiconductor / Motorola

Freescale Semiconductor, Inc.
Changing DESIRED_POSITION in Mid-Move
9.2
Changing DESIRED_POSITION in Mid-Move
Because DESIRED_POSITION is re-evaluated against CURRENT_POSITION after every step,
DESIRED_POSITION can be changed by the CPU at any time during a move. This feature is particularly
important for fast servo systems. A move request HSR should always be issued when
DESIRED_POSITION is changed. There are four possible cases for a changed DESIRED_POSITION
value -- the TSM function responds differently in each case.
Case 1: New DESIRED_POSITION is in the same direction as old DESIRED_POSITION but further away.
See Figure 9a.
If the motor is slewing, this phase of the move is extended until it is time to decelerate to the new
DESIRED_POSITION.
If the motor has started to decelerate, the new DESIRED_POSITION may result in additional acceleration
and further slew phase.
Case 2: New DESIRED_POSITION is in the same direction as old DESIRED_POSITION but closer. See
Figure 9b.
If the motor is not closer to the new DESIRED_POSITION than the number of acceleration steps already
taken, the motor continues to accelerate and slew until it is time to decelerate to the new
DESIRED_POSITION.
If the motor is closer to the new DESIRED_POSITION than the number of acceleration steps already taken,
the motor immediately decelerates. This causes overshoot, the motor will subsequently reverse direction and
accelerate (if possible) to the new DESIRED_POSITION.
Case 3: New DESIRED_POSITION is in opposite direction to CURRENT_POSITION than old
DESIRED_POSITION. See Figure 9c.
The motor immediately decelerates, and when it reaches START_PERIOD, it reverses direction and
accelerates/slews/decelerates to the new DESIRED_POSITION.
Case 4: New DESIRED_POSITION is the same as CURRENT_POSITION. See Figure 9d.
If the last step had a period equal to START_PERIOD, then the function stops and issues an interrupt
request.
If the last step was not at the start/stop rate, the motor immediately decelerates. This causes overshoot, and
the motor will subsequently reverse direction and accelerate (if possible) to the new DESIRED_POSITION.
24
Using the Table Stepper Motor TPU Function
MOTOROLA
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