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This TPU Programming Note is intended to provide simple C interface routines to the
programmable time accumulator TPU function (PTA).
1
The routines are targeted for the
MPC500 family of devices, but they should be easy to use with any device that has a TPU.
1 Functional Overview
This TPU input function measures the total high time, low time or period of an input signal
over a user defined number of periods, and presents the result to the host CPU in the form of
a 32-bit accumulation.
2 Detailed Description
The programmable time accumulator (PTA) function measures either period, high time or low
time of an input signal over a programmable number of periods. The number of periods over
which the measurement is made is selectable over the range 1 to 255. Four modes of
measurement are available:
• Mode 1 measures total high time over the selected number of periods.
• Mode 2 measures total low time over the selected number of periods.
• Mode 3 measures total period over the selected number of periods, starting on a
rising edge.
• Mode 4 measures total period over the selected number of periods, starting on a
falling edge.
Figure 1 shows the four operating modes. All four examples are based on an accumulation of
seven periods, which are numbered below each waveform. Dark shaded areas in the bar below
each waveform indicate which parts of the waveform are actually measured. Unshaded areas
are not included in the measurement. Lightly shaded areas are part of the next measurement
cycle.
The output of the PTA function is a 32-bit result, which is expressed in counts of the selected
TPU timebase. The user can select either TCR1 or TCR2 as the timebase for the measurement.
The number of TCR counts that have been accumulated multiplied by the period of one TCR
count will give the total measurement expressed in seconds.
1
The information in this Programming Note is based on TPUPN06. It is intended to
compliment the information found in that Programming Note.
Application Note
AN2365/D
Rev. 0, 10/2002
Using the
Programmable Time
Accumulator TPU
Function (PTA) with the
MPC500 Family
Stan Ostrum
Metrowerks
Freescale Semiconductor, I
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