
Timing System
Input Capture
MC68HC11E Family
—
Rev. 4
Technical Data
MOTOROLA
Timing System
183
to result in input captures. Writing to TI4/O5 has no effect when the
TI4/O5 register is acting as IC4.
9.4.1 Timer Control Register 2
Use the control bits of this register to program input capture functions to
detect a particular edge polarity on the corresponding timer input pin.
Each of the input capture functions can be independently configured to
detect rising edges only, falling edges only, any edge (rising or falling),
or to disable the input capture function. The input capture functions
operate independently of each other and can capture the same TCNT
value if the input edges are detected within the same timer count cycle.
EDGxB and EDGxA
—
Input Capture Edge Control Bits
There are four pairs of these bits. Each pair is cleared to 0 by reset
and must be encoded to configure the corresponding input capture
edge detector circuit. IC4 functions only if the I4/O5 bit in the PACTL
register is set. Refer to
Table 9-2
for timer control configuration.
Address:
$1021
Bit 7
6
5
4
3
2
1
Bit 0
Read:
EDG4B
EDG4A
EDG1B
EDG1A
EDG2B
EDG2A
EDG3B
EDG3A
Write:
Reset:
0
0
0
0
0
0
0
0
Figure 9-3. Timer Control Register 2 (TCTL2)
Table 9-2. Timer Control Configuration
EDGxB
EDGxA
Configuration
0
0
Capture disabled
0
1
Capture on rising edges only
1
0
Capture on falling edges only
1
1
Capture on any edge