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MC68F375
CONFIGURABLE TIMER MODULE (CTM9)
MOTOROLA
REFERENCE MANUAL
Rev. 25 June 03
13-29
Figure 13-9 DASM Input Capture Example
13.5.2.5 Output Compare (OCB and OCAB) Modes
OC mode is selected by making MODE[3:0] = 010x. The MODE0 bit controls the set-
ting criteria for the FLAG bit, i.e. when a compare occurs only on channel B or when a
This mode allows the DASM to perform four different output functions:
Single-shot output pulse (two edges), with FLAG set on the second edge.
Single-shot output pulse (two edges), with FLAG set on both edges.
Single-shot output transition (one edge).
Output port pin, with output compare function disabled.
In this mode the leading and trailing edges of variable width output pulses are gener-
ated by calculated output compare events occurring on channels A and B,
respectively. OC mode may also be used to perform a single output compare function,
similar to the M68HC11 timer, or may be used as an output port bit.
In this mode, channel B is accessed via register B2. Register B1 is not used and is not
accessible to the user. Both channels work together to generate one ‘single shot’ out-
put pulse signal. Channel A defines the leading edge of the output pulse, while channel
B defines the trailing edge of the pulse. FLAG setting can be done when a compare
occurs on channel B only or when a compare occurs on either channel (as defined by
the MODE0 bit in the DASMSIC register).
When this mode is first selected, both comparators are disabled. Each comparator is
enabled by writing to its data register; it remains enabled until the next successful com-
parison is made on that channel, whereupon it is disabled. The values stored in
registers A and B are compared with the count value on the selected time base bus
when their corresponding comparators are enabled.
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
FLAG reset
by software
1. These values are accessible to the software.
2. These values are internal and are not accessible.
Notes:
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