
MC68F375
CONFIGURABLE TIMER MODULE (CTM9)
MOTOROLA
REFERENCE MANUAL
Rev. 25 June 03
13-28
sequence of events is repeated for each subsequent capture. Reading data register B
returns the value in register B2.
If a 32-bit coherent operation is in progress when an edge is detected, the transfer of
data from B1 to B2 is deferred until the coherent operation is completed. At any time,
the input level present on the input pin can be read on the IN bit.
The input pulse period is calculated by subtracting the value in data register B from the
value in data register A.
Figure 13-8 provides an example of how the DASM can be used for input period
measurement.
Figure 13-8 Input Period Measurement Example
13.5.2.4 Input Capture (IC) Mode
IC mode is selected by making MODE[3:0] = 0011.
This mode is identical to the input period measurement mode (IPM) described above,
with the exception that the FLAG bit is also set at the occurrence of the first detected
edge of the selected polarity. In this mode the DASM functions as a standard input
capture function in a similar way to the M68HC11 family timers. In this case the value
latched in channel B can be ignored.
Figure 13-9 provides an example of how the DASM can be used for input capture.
Time base bus
0x0500
0x1000
0x1100
0x1250
0x1525
0x16A0
FLAG bit
DASMA captured value1
B1 value2
B2 value1
0xxxxx
0x1000
0x1250
0x16A0
0xxxxx
0x1000
0x1250
0x16A0
0xxxxx
0x1000
0x1250
Input signal
Mode selection; EDPOL = 0
FLAG reset
by software
FLAG reset
by software
AA
A
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Freescale Semiconductor, Inc.
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