Datasheet

I/O Registers
MC68HC908JL3E Family Data Sheet, Rev. 4
Freescale Semiconductor 93
MSxB — Mode Select Bit B
This read/write bit selects buffered output compare/PWM operation. MSxB exists only in the TIM
channel 0 status and control register. Setting MS0B disables the channel 1 status and control register
and reverts TCH1 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:ELSxA ≠ 0:0, this read/write bit selects either input capture operation or unbuffered
output compare/PWM operation. See Table 8-3.
1 = Unbuffered output compare/PWM operation
0 = Input capture operation
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.
NOTE
Before enabling a TIM channel register for input capture operation, make
sure that the TCHx pin is stable for at least two bus clocks.
Table 8-3. Mode, Edge, and Level Selection
MSxB MSxA ELSxB ELSxA Mode Configuration
X0 0 0
Output Preset
Pin under Port Control; Initial Output Level High
X 1 0 0 Pin under Port Control; Initial Output Level Low
00 0 1
Input Capture
Capture on Rising Edge Only
0 0 1 0 Capture on Falling Edge Only
0 0 1 1 Capture on Rising or Falling Edge
01 0 1
Output
Compare or
PWM
Toggle Output on Compare
0 1 1 0 Clear Output on Compare
0 1 1 1 Set Output on Compare
1X 0 1
Buffered Output
Compare or
Buffered
PWM
Toggle Output on Compare
1 X 1 0 Clear Output on Compare
1 X 1 1 Set Output on Compare