MC68HC908AT32 Datasheet, PDF (216/378 Pages) Freescale Semiconductor, Inc – Microcontrollers

Timer Interface (TIMB)
MSxA — Mode Select Bit A
When ELSxB:A ≠ 00, this read/write bit selects either input capture operation or unbuffered output
compare/PWM operation. (See Table 19-2.)
1 = Unbuffered output compare/PWM operation
0 = Input capture operation
When ELSxB:A = 00, this read/write bit selects the initial output level of the TCHx pin once PWM, input
capture, or output compare operation is enabled. (See Table 19-2.). 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 TIMB status and control register (TBSC).
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/TBCHx or pin PTFx/TBCHx 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 19-2 shows how ELSxB and ELSxA work. Reset
clears the ELSxB and ELSxA bits.
NOTE
Before enabling a TIMB channel register for input capture operation, make
sure that the PTEx/TBCHx pin or PTFx/TBCHx pin is stable for at least two
bus clocks.
Table 19-2. Mode, Edge, and Level Selection
MSxB:MSxA
X0
X1
00
00
00
01
01
01
1X
1X
1X
ELSxB:ELSxA
00
00
01
10
11
01
10
11
01
10
11
Mode
Configuration
Output
preset
Pin under port control;
Initialize timer
Output level high
Pin under port control;
Initialize timer
Output level low
Input
capture
Capture on rising edge only
Capture on falling edge only
Capture on rising or falling edge
Output
compare
or PWM
Toggle output on compare
Clear output on compare
Set output on compare
Buffered
Toggle output on compare
output compare Clear output on compare
or buffered PWM _{Set output on compare}
MC68HC908AT32 Data Sheet, Rev. 3.1
216
Freescale Semiconductor