MC908QT4MPE datasheet(131/184 Pages) FREESCALE

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Input/Output Registers

MC68HC908QY/QT Family Data Sheet, Rev. 5

Freescale Semiconductor

131

When ELSxB:A = 00, this read/write bit selects the initial output level of the TCHx pin (see Table 14-3).

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 14-3 shows how ELSxB and ELSxA work. Reset clears

the ELSxB and ELSxA bits.

NOTE

After initially 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.

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 14-3. Mode, Edge, and Level Selection

MSxB

MSxA

ELSxB

ELSxA

Mode

Configuration

Output preset

Pin under port control; initial output level high

Pin under port control; initial 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

Software compare only

Toggle output on compare

Clear output on compare

Set output on compare

Buffered output

compare or

buffered PWM

Toggle output on compare

Clear output on compare

Set output on compare

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