Timer Interface (TIM)
Data Sheet
MC68HC08AS32A — Rev. 1
258
Timer Interface (TIM)
MOTOROLA
ELSxB and ELSxA — Edge/Level Select Bits
When channel x is an input capture channel, these read/write bits control the
active edge-sensing logic on channel x.
When channel x is an output compare channel, ELSxB and ELSxA control the
channel x output behavior when an output compare occurs.
When ELSxB and ELSxA are both clear, channel x is not connected to port E or
port F, and pin PTEx/TCHx or pin PTFx/TCHx is available as a general-purpose
I/O pin. However, channel x is at a state determined by these bits and becomes
transparent to the respective pin when PWM, input capture, or output compare
mode is enabled.
Table 16-2
shows how ELSxB and ELSxA work. Reset clears
the ELSxB and ELSxA bits.
NOTE:
Before enabling a TIM channel register for input capture operation, make sure that
the PTEx/TCHx pin or PTFx/TCHx pin is stable for at least two bus clocks.
TOVx — Toggle-On-Overflow Bit
When channel x is an output compare channel, this read/write bit controls the
behavior of the channel x output when the TIM counter overflows. When
channel x is an input capture channel, TOVx has no effect. Reset clears the
TOVx bit.
1 = Channel x pin toggles on TIM counter overflow.
0 = Channel x pin does not toggle on TIM counter overflow.
NOTE:
When TOVx is set, a TIM counter overflow takes precedence over a channel x
output compare if both occur at the same time.
Table 16-2. Mode, Edge, and Level Selection
MSxB–MSxA
ELSxB–ELSxA
Mode
Configuration
X0
00
Output Preset
Pin under Port Control;
Initialize Timer
Output Level High
X1
00
Pin under Port Control;
Initialize Timer
Output Level Low
00
01
Input Capture
Capture on Rising Edge Only
00
10
Capture on Falling Edge Only
00
11
Capture on Rising or Falling Edge
01
01
Output Compare
or PWM
Toggle Output on Compare
01
10
Clear Output on Compare
01
11
Set Output on Compare
1X
01
Buffered
Output Compare
or Buffered PWM
Toggle Output on Compare
1X
10
Clear Output on Compare
1X
11
Set Output on Compare
F
Freescale Semiconductor, Inc.
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Go to: www.freescale.com
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