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8-BIT TIMER A/B S3C8245/P8245/C8249/P8249
11-2
FUNCTION DESCRIPTION
Timer A Interrupts (IRQ0, Vectors E0H and E2H)
The timer A module can generate two interrupts: the timer A overflow interrupt (TAOVF), and the timer A match/
capture interrupt (TAINT). TAOVF is interrupt level IRQ0, vector E2H. TAINT also belongs to interrupt level IRQ0, but
is assigned the separate vector address, E0H.
Pending condition of timer A interrupts (overflow & match/capture) can be cleared automatically by hardware where
the interrupts are enabled. Otherwise pending condition must be cleared manually by software.
Interval Timer Function
The timer A module can generate an interrupt: the timer A match interrupt (TAINT). TAINT belongs to interrupt level
IRQ0, and is assigned the separate vector address, E0H.
When timer A match interrupt occurs and is serviced by the CPU, the pending condition is cleared automatically by
hardware.
In interval timer mode, a match signal is generated and TAOUT is toggled when the counter value is identical to the
value written to the TA reference data register, TADATA. The match signal generates a timer A match interrupt
(TAINT, vector E0H) and clears the counter.
If, for example, you write the value 10H to TADATA and 0AH to TACON, the counter will increment until it reaches
10H. At this point, the TA interrupt request is generated, the counter value is reset, and counting resumes.
Pulse Width Modulation Mode
Pulse width modulation (PWM) mode lets you program the width (duration) of the pulse that is output at the TAPWM
pin. As in interval timer mode, a match signal is generated when the counter value is identical to the value written to
the timer A data register. In PWM mode, however, the match signal does not clear the counter. Instead, it runs
continuously, overflowing at FFH, and then continues incrementing from 00H.
Although timer A overflow interrupt is occurred, this interrupt is not typically used in PWM-type applications. Instead,
the pulse at the TAPWM pin is held to Low level as long as the reference data value is less than or equal to ( ≤ ) the
counter value and then the pulse is held to High level for as long as the data value is greater than ( > ) the counter
value. One pulse width is equal to t
CLK
• 256 .
Capture Mode
In capture mode, a signal edge that is detected at the TACAP pin opens a gate and loads the current counter value
into the TA data register. You can select rising or falling edges to trigger this operation.
Timer A also gives you capture input source: the signal edge at the TACAP pin. You select the capture input by
setting the value of the timer A capture input selection bit in the port 3 control register, P3CONL, (set 1, bank 0,
E9H). When P3CONL.7.6 is 00, the TACAP input or normal input is selected. When P3CONL.7.6 is set to 11,
normal output is selected.
Both kinds of timer A interrupts can be used in capture mode: the timer A overflow interrupt is generated whenever a
counter overflow occurs; the timer A match/capture interrupt is generated whenever the counter value is loaded into
the TA data register.
By reading the captured data value in TADATA, and assuming a specific value for the timer A clock frequency, you
can calculate the pulse width (duration) of the signal that is being input at the TACAP pin.