mc68hc11d0cfn2 Freescale Semiconductor, Inc, mc68hc11d0cfn2 Datasheet - Page 102

• Manufacturer Part Number: mc68hc11d0cfn2
• Description: M68hc11 Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

Programmable Timer
8.4 Output Compare (OC)
Data Sheet
102
Use the output compare (OC) function to program an action to occur at a specific
time — when the 16-bit counter reaches a specified value. For each of the five
output compare functions, there is a separate 16-bit compare register and a
dedicated 16-bit comparator. The value in the compare register is compared to the
value of the free-running counter on every bus cycle. When the compare register
matches the counter value, an output compare status flag is set. The flag can be
used to initiate the automatic actions for that output compare function.
To produce a pulse of a specific duration, write to the output compare register a
value representing the time the leading edge of the pulse is to occur. The output
compare circuit is configured to set the appropriate output either high or low,
depending on the polarity of the pulse being produced. After a match occurs, the
output compare register is reprogrammed to change the output pin back to its
inactive level at the next match. A value representing the width of the pulse is
added to the original value, and then is written to the output compare register.
Because the pin state changes occur at specific values of the free-running counter,
the pulse width can be controlled accurately at the resolution of the free-running
counter, independent of software latencies. To generate an output signal of a
specific frequency and duty cycle, repeat this pulse-generating procedure.
There are four 16-bit read/write output compare registers: TOC1, TOC2, TOC3,
and TOC4, and the TI4/O5 register, which functions under software control as
either IC4 or OC5. Each of the OC registers is set to $FFFF on reset. A value
written to an OC register is compared to the free-running counter value during each
E-clock cycle. If a match is found, the particular output compare flag is set in timer
interrupt flag register 1 (TFLG1). If that particular interrupt is enabled in the timer
interrupt mask register 1 (TMSK1), an interrupt is generated. In addition to an
interrupt, a specified action can be initiated at one or more timer output pins. For
OC5–OC2, the pin action is controlled by pairs of bits (OMx and OLx) in the TCTL1
register. The output action is taken on each successful compare, regardless of
whether the OCxF flag in the TFLG1 register was previously cleared.
OC1 is different from the other output compares in that a successful OC1 compare
can affect any or all five of the OC pins. The OC1 output action taken when a match
is found is controlled by two 8-bit registers with three bits unimplemented: the
output compare 1 mask register, OC1M, and the output compare 1 data register,
OC1D. OC1M specifies which port A outputs are to be used, and OC1D specifies
what data is placed on these port pins.
Freescale Semiconductor, Inc.
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Programmable Timer
MC68HC711D3 — Rev. 2
MOTOROLA