Freescale Semiconductor MC68HC908MR32 - Manual (Page 230)

Timer Interface A (TIMA)
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1
230 Freescale Semiconductor
MSxB — Mode Select Bit B
This read/write bit selects buffered output compare/PWM operation. MSxB exists only in the TIMA
channel 0 and TIMA channel 2 status and control registers.
Setting MS0B disables the channel 1 status and control register and reverts TCH1A pin to
general-purpose I/O.
Setting MS2B disables the channel 3 status and control register and reverts TCH3A pin to
general-purpose I/O.
Reset clears the MSxB bit.
1 = Buffered output compare/PWM operation enabled
0 = Buffered output compare/PWM operation disabled
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 16-2 .
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 TCHxA pin once PWM,
input capture, or output compare operation is enabled. See
Table 16-2 . 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 TIMA status and control register (TASC).
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, and pin PTEx/TCHxA
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 TIMA channel register for input capture operation, make
sure that the PTEx/TACHx pin is stable for at least two bus clocks.