MC68HC908JW32_09 Datasheet, PDF (119/232 Pages) Freescale Semiconductor, Inc – M68HC08 Microcontrollers

I/O Registers
When ELSxB:ELSxA = 0:0, this read/write bit selects the initial output level of the TCHx pin. See
Table 8-3. Reset clears the MSxA bit.
1 = Initial output level low
0 = Initial output level high
NOTE
Before changing a channel function by writing to the MSxB or MSxA bit, set
the TSTOP and TRST bits in the TIM status and control register (TSC).
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 an I/O port, and pin TCHx is
available as a general-purpose I/O pin. Table 8-3 shows how ELSxB and ELSxA work. Reset clears
the ELSxB and ELSxA bits.
Table 8-3. Mode, Edge, and Level Selection
MSxB:MSxA
X0
X1
00
00
00
01
01
01
01
1X
1X
1X
ELSxB:ELSxA
00
00
01
10
11
00
01
10
11
01
10
11
Mode
Output preset
Input capture
Output compare
or PWM
Buffered output
compare or
buffered PWM
Configuration
Pin under port control;
initial output level high
Pin under port control;
initial output level low
Capture on rising edge only
Capture on falling edge only
Capture on rising or
falling edge
Software compare only
Toggle output on compare
Clear output on compare
Set output on compare
Toggle output on compare
Clear output on compare
Set output on compare
NOTE
After iniitially enabling a TIM channel register for input capture operation,
and selecting the edge sensitivity, clear CHxF to ignore any erroneous
edge detection flags.
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
MC68HC908JW32 Data Sheet, Rev. 6
Freescale Semiconductor
119