FUNCTIONAL DEVICE OPERATION
OPERATIONAL MODES
FUNCTIONAL DEVICE OPERATION
OPERATIONAL MODES
STATE MACHINE OPERATION
The 33977 is ideal for use in instrumentation systems
requiring distributed and flexible stepper motor gauge driving.
The device also eases the transition to stepper motors from
air core motors by emulating the air core pointer movement
with little additional processor bandwidth utilization. The two-
phase stepper motor has maximum allowable velocities and
acceleration and deceleration. The purpose of the stepper
motor state machine is to drive the motor with the maximum
performance while remaining within the motor’s voltage,
velocity, and acceleration constraints.
A requirement of the state machine is to ensure the
deceleration phase begins at the correct time and pointer
position. When commanded, the motor [will deleted PV]
accelerates constantly to the maximum velocity, and then it
moves toward the commanded position at the maximum
velocity. Eventually, the pointer reaches the calculated
location where the movement has to decelerate, safely
slowing to a stop at the desired position. During the
deceleration phase, the motor does [will deleted PV] not
exceed the maximum deceleration.
During normal operation, both stepper motor rotors are
microstepped at 24 steps per electrical revolution, illustrated
in Figure 7. A complete electrical revolution results in two
degrees of pointer movement. There is a second smaller
[parentheses removed-unnecessary] state machine in the IC
controlling these microsteps. The smaller state machine
receives clockwise or counter-clockwise index commands at
timed intervals, thereby stepping the motor in the appropriate
direction by adjusting the current in each coil. Normalized
values are provided in Table 5.
Figure 7. Clockwise Microsteps
Table 5. Coil Step Value
SINE
(Angle)*
COS (Angle -30)* COS (Angle -30)*
Step
Angle
PE6=0
PE6=1
0.866
0.966
1.0
0
1
0.0
15
0.0
1.0
0.259
0.5
0.965
0.866
0.707
0.5
2
30
3
45
0.707
0.866
0.966
1.0
0.966
0.866
0.707
0.500
0.259
0.0
4
60
5
75
0.259
0.0
6
90
7
105
120
135
150
0.966
0.866
0.707
0.5
-0.259
-0.5
8
9
-0.707
-0.866
-0.259
-0.500
10
33977
Analog Integrated Circuit Device Data
Freescale Semiconductor
12
FREESCALE [ Freescale ]
