AN2367 Freescale Semiconductor / Motorola, AN2367 Datasheet - Page 5

• Manufacturer Part Number: AN2367
• Description: Using the Multiphase Motor Commutation TPU Function (COMM)with the MPC500 Family
• Manufacturer: Freescale Semiconductor / Motorola

Freescale Semiconductor, Inc.
All Modes
The COMM function directly accesses this counter, located anywhere in parameter RAM, and performs
tests on it to determine the required state of the commutation output pins. This process is carried out without
CPU intervention. The COMM function maintains upper and lower angular limits to the current state in
parameter RAM. On each service of the COMM function, the position counter is compared with these
limits. If the position count has passed either limit, the state number is updated and a new state parameter is
obtained from a circular table in parameter RAM. The state parameter contains the pin configuration and
length of the new state in position counts. New upper and lower angular limits are calculated using the
length of the new state and then stored for use in subsequent state tests. The new pin configuration is
subsequently output on the COMM channels.
As an additional feature of sensorless operation, a CPU supplied angular offset is added to the position count
before the limit tests. This parameter, which can be updated at any time, allows the CPU to advance or retard
previously programmed state switching angles. The offset parameter can be used to start the motor in a
particular direction, to partially compensate for TPU service latencies, to maintain torque at high motor
speeds, and to force braking on the motor.
The number of states in the commutation sequence, the length in angular position counts of each state, the
number of channels used for commutation, and the pin states for each state are all independently
programmable by the user. These capabilities make the function suitable for a wide variety of commutation
schemes.
On the original TPU, the layout of the parameter RAM places some restrictions on the maximum table size,
dependent on which channel is selected as the master channel. These restrictions are described in TPUPN09.
The TPU3 on the MPC555, with eight parameters per channel does impose the same restrictions and the
maximum table size does not depend on which channel is selected as the master.
Up to eight TPU channels can be used as COMM signal outputs (including the master channel), and each
state has a length which is individually programmable over an 8 bit range in position counts. In applications
using an encoder with a very high resolution, an 8-bit range for the state length in position counts may not
be sufficient. COMM allows the use of multiple state table entries programmed to have the same output pin
configuration, to effectively lengthen the state.
In sensorless operation, the COMM function has been designed to update the commutation signals on a
periodic basis, and there are two "sub-modes" of operation. These are Match Update and Link Update. Only
Match Update is supported by the C interface routines.
In this mode, a user programmable periodic match on the master COMM channel is used to invoke updating
of the commutation signals. Assuming an accurate position encoder, the accuracy of commutation is
dependent on this periodic update rate. A faster update rate results in more accurate commutation, but a
higher TPU overhead. This mode is for use with the QDEC or FQD TPU input functions.
2.3
All Modes
The host CPU can force any commutation state, to put the motor stator field into a known configuration, at
any time. The CPU can also interrogate the COMM function at any time to determine which state is
currently active. Since the state table is programmed during initialization, the user can decide which state
number corresponds to which output pin configuration. This flexibility allows a variety of commutation
schemes to be implemented.
To drive the motor, the outputs of the COMM function TPU channels will be used to gate a PWM generated
on another TPU channel onto the motor phase drivers.
MOTOROLA
Using the Multiphase Motor Commutation TPU Function
5
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