Information

36.4.2 Interrupts
All the timers support interrupt generation. See the MCU specification for related vector
addresses and priorities.
Timer interrupts can be enabled by setting TCTRLn[TIE]. TFLGn[TIF] are set to 1 when
a timeout occurs on the associated timer, and are cleared to 0 by writing a 1 to the
corresponding TFLGn[TIF].
36.5 Initialization and application information
In the example configuration:
• The PIT clock has a frequency of 50 MHz.
• Timer 1 creates an interrupt every 5.12 ms.
• Timer 3 creates a trigger event every 30 ms.
The PIT module must be activated by writing a 0 to MCR[MDIS].
The 50 MHz clock frequency equates to a clock period of 20 ns. Timer 1 needs to trigger
every 5.12 ms/20 ns = 256,000 cycles and Timer 3 every 30 ms/20 ns = 1,500,000 cycles.
The value for the LDVAL register trigger is calculated as:
LDVAL trigger = (period / clock period) -1
This means LDVAL1 and LDVAL3 must be written with 0x0003E7FF and 0x0016E35F
respectively.
The interrupt for Timer 1 is enabled by setting TCTRL1[TIE]. The timer is started by
writing 1 to TCTRL1[TEN].
Timer 3 shall be used only for triggering. Therefore, Timer 3 is started by writing a 1 to
TCTRL3[TEN]. TCTRL3[TIE] stays at 0.
The following example code matches the described setup:
// turn on PIT
PIT_MCR = 0x00;
// Timer 1
PIT_LDVAL1 = 0x0003E7FF; // setup timer 1 for 256000 cycles
PIT_TCTRL1 = TIE; // enable Timer 1 interrupts
PIT_TCTRL1 |= TEN; // start Timer 1
// Timer 3
Chapter 36 Periodic Interrupt Timer (PIT)
K20 Sub-Family Reference Manual, Rev. 2, Feb 2012
Freescale Semiconductor, Inc. 825