National CP3BT26 - Manual (Page 202)

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CP3BT26
26.3 TIMER INTERRUPTS
The Multi-Function Timer unit has four interrupt sources,
designated A, B, C, and D. Interrupt sources A, B, and C are
mapped into a single system interrupt called Timer Interrupt
1, while interrupt source D is mapped into a system interrupt
called Timer Interrupt 2. Each of the four interrupt sources
has its own enable bit and pending bit. The enable bits are
named TAIEN, TBIEN, TCIEN, and TDIEN. The pending
bits are named TAPND, TBPND, TCPND, and TDPND.
Timer Interrupts 1 and 2 are system interrupts TA and TB
(IRQ14 and IRQ13), respectively.
Table 77 shows the events that trigger interrupts A, B, C,
and D in each of the four operating modes. Note that some
interrupt sources are not used in some operating modes.
26.4 TIMER I/O FUNCTIONS
The Multi-Function Timer unit uses two I/O pins, called TA
and TB. The function of each pin depends on the timer op-
erating mode and the TAEN and TBEN enable bits. Table 78
shows the functions of the pins in each operating mode, and
for each combination of enable bit settings.
When the TA pin is configured to operate as a PWM output
(TAEN = 1), the state of the pin is toggled on each underflow
of the TCNT1 counter. In this case, the initial value on the
pin is determined by the TAOUT bit. For example, to start
with TA high, software must set the TAOUT bit before en-
abling the timer clock. This option is available only when the
timer is configured to operate in Mode 1, 3, or 4 (in other
words, when TCRA is not used in Capture mode).
Table 77 Timer Interrupts Overview
Sys. Int.
Interrupt
Pending
Bit
Mode 1 Mode 2 Mode 3 Mode 4
PWM + Counter
Dual Input Capture +
Counter
Dual Counter
Single Capture +
Counter
Timer
Int. 1
(TA Int.) TAPND TCNT1 reload from
TCRA Input capture on TA
transition TCNT1 reload from
TCRA TCNT1 reload from
TCRA
TBPND TCNT1 reload from
TCRB Input Capture on TB
transition N/A Input Capture on TB
transition
TCPND N/A TCNT1 underflow N/A N/A
Timer
Int. 2
(TB Int.) TDPND TCNT2 underflow TCNT2 underflow TCNT2 reload from
TCRB TCNT2 underflow
Table 78 Timer I/O Functions
I/O
TAEN
TBEN
Mode 1 Mode 2 Mode 3 Mode 4
PWM + Counter
Dual Input Capture +
counter
Dual Counter
Single Capture +
counter
TA TAEN = 0
TBEN = X No Output Capture TCNT1 into
TCRA No Output Toggle No Output Toggle
TAEN = 1
TBEN = X Toggle Output on
Underflow of TCNT1 Capture TCNT1 into
TCRA and Preset
TCNT1 Toggle Output on
Underflow of TCNT1 Toggle Output on
Underflow of TCNT1
TB TAEN = X
TBEN = 0 Ext. Event or Pulse
Accumulate Input Capture TCNT1 into
TCRB Ext. Event or Pulse
Accumulate Input Capture TCNT2 into
TCRB
TAEN = X
TBEN = 1 Ext. Event or Pulse
Accumulate Input Capture TCNT1 into
TCRB and Preset
TCNT1 Ext. Event or Pulse
Accumulate Input Capture TCNT2 into
TCRB and Preset
TCNT2