Interrupt and DMA Triggers

The Universal Timer module provides three interrupt sources – Period Register match, Zero and Capture.

  1. 1.A PR match interrupt occurs and the PRIF interrupt flag in the TUxyCON1 register is set when the TUxyTMR counter register increments and becomes equal to the TUxyPR period register. The PRIF interrupt will not occur if the user writes the PR value to the TUxyTMR counter register directly.
  2. 2.A zero interrupt occurs and the ZIF interrupt flag in the TUxyCON1 register is set when the TUxyTMR counter register becomes equal to zero. This occurs when:
    • A Reset condition resets the counter to zero, or
    • Software sets the CLR command bit, or
    • Counter naturally overflows to zero, or
    • User writes zero to the TUxyTMR counter register directly
  3. 3.A capture interrupt occurs and the CIF interrupt flag in the TUxyCON1 register is set whenever a capture event occurs, and the TUxyCR capture register is updated with the counter value. See Timer Counter and Capture Registers for a list of capture event conditions. The CIF interrupt trigger requires a running timer.
Each interrupt has a corresponding enable bit (PRIE, ZIE and CIE) in the TUxyCON0 register. Setting any of the three interrupt enable bits will allow the module to generate a corresponding interrupt. The interrupt flags (PRIF, ZIF and CIF) will set even if the corresponding interrupt is disabled.

All the three interrupt flags are combined together to form one single, top system level TUxyIF interrupt flag in the PIRx register, as shown in Figure 1. The TUxyIF interrupt flag is a read-only bit in the PIRx register, which is automatically cleared when all the three interrupt flags (PRIF, ZIF and CIF) are cleared.

The Universal Timer module also provides the three interrupt sources to trigger DMA transfers (PRIF, ZIF and CIF conditions). The TUxyPR period register is also double-buffered to facilitate DMA loading of the register in response to a CIF interrupt trigger.

Important:
  1. 1.The interrupts need not be enabled with their associated enable bits to be used as triggers for DMA transfer.
  2. 2.The interrupts must be enabled for the TUxyIF flag to be set in the PIRx register as shown in Figure 1.
Figure 1. Interrupt and DMA Trigger