User`s guide

LZ87010 Advance User’s Guide Interrupts
1/15/03 12-3
12.1.2.1 Vectors and Status Bits
An interrupt vector that is shared between two or more interrupt sources requires a status
register so the interrupt handler can determine which interrupt was asserted. For example,
Timer 2 has five interrupt sources that are handled by a single vector. The T2STA register
contains a bit for each interrupt source, allowing the interrupt handler to determine which
sources are active.
An interrupt source that has a vector to itself does not require a status bit. The fact that the
interrupt handler has been called indicates that the interrupt has been asserted. For this
reason, some interrupts do not have status at all, and others have status bits that are
cleared upon entry to the associated interrupt handler. In the latter case, the interrupt
status bits can be used when polling is preferred to interrupts.