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MC68F375
CONFIGURABLE TIMER MODULE (CTM9)
MOTOROLA
REFERENCE MANUAL
Rev. 25 June 03
13-27
If a 32-bit coherent operation is in progress when the falling edge is detected, the
transfer from B1 to B2 is deferred until the coherent operation is completed. Operation
of the DASM then continues on channels B and A as previously described.
The input pulse width is calculated by subtracting the value in data register B from the
value in data register A.
Figure 13-7 provides an example of how the DASM can be used for input pulse width
measurement.
Figure 13-7 Input Pulse Width Measurement Example
13.5.2.3 Input Period Measurement (IPM) Mode
IPM mode is selected by making MODE[3:0] = 0010.
This mode allows the period of an input signal to be determined by capturing two con-
secutive rising edges or two consecutive falling edges; successive input captures are
done on consecutive edges of the same polarity. The edge polarity is defined by the
EDPOL bit in the DASMSIC register.
This mode also allows the software to determine the logic level on the input pin at any
time by reading the IN bit in the DASMSIC register.
When the first edge having the selected polarity is detected, the time base bus value
is latched into the 16-bit data register A, the data in register B1 is transferred to data
register B2 and finally the data in register A is transferred to register B1. On this first
capture the FLAG bit is not set. On the second and subsequent captures, the FLAG
bit is set immediately before the data in register A is transferred to register B1.
When the second edge of the same polarity is detected, the time base bus value is
latched into data register A, the data in register B1 is transferred to data register B2,
the FLAG bit is set to signify that the beginning and end points of a complete period
have been captured, and finally data register A is transferred to register B1. This
Time base bus
0x0500
0x1000
0x1100
0x1250
0x1525
0x16A0
FLAG bit
DASMA captured value1
B1 captured value2
B2 value1
0xxxxx
0x1000
0x1250
0x16A0
0xxxxx
0x1100
0x1525
0xxxxx
0x1000
0x1250
Input signal
Mode selection; EDPOL = 1
FLAG reset
by software
FLAG reset
by software
BA
BAB
1. These values are accessible to the software.
2. These values are internal and are not accessible.
Notes:
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