Interrupt Selector Registers
13-7
Interrupt Selector and External Interrupts
13.3 Interrupt Selector Registers
Table 13–3 shows the interrupt selector registers. The interrupt multiplexer
registers determine the mapping between the interrupt sources in Table 13–1
and the CPU interrupts 4 through 15 (INT4–INT15). The external interrupt
polarity register sets the polarity of external interrupts.
Table 13–3. Interrupt Selector Registers
Byte
Address
Name
Description
Section
019C0000h
Interrupt multiplexer high
Selects which interrupts drive CPU interrupts 10–15
(INT10–15)
13.3.2
019C0004h
Interrupt multiplexer low
Selects which interrupts drive CPU interrupts 4–9
(INT4–INT9)
13.3.2
019C0008h
External interrupt polarity
Sets the polarity of the external interrupts
(EXT_INT4–EXT_INT7)
13.3.1
13.3.1 External Interrupt Polarity Register
The external interrupt polarity register allows you to change the polarity of the
four external interrupts (EXT_INT4 to EXT_INT7). When XIP is its default value
of 0, a low-to-high transition on an interrupt source is recognized as an interrupt.
By setting the related XIP bit in this register to 1, you can invert the external inter-
rupt source and effectively have the CPU detect high-to-low transitions of the
external interrupt. Changing an XIP bit’s value creates transitions on the related
CPU interrupt (INT4–INT15) that the external interrupt, EXT_INT, is selected to
drive. For example, if XIP4 is changed from 0 to 1 and EXT_INT4 is low, or if
XIP4 is changed from 1 to 0 and EXT_INT4 is high, the CPU interrupt that is
mapped to EXT_INT4 becomes set. The external interrupt polarity register only
affects interrupts to the CPU, and has no effect on DMA events.
Figure 13–2. External Interrupt Polarity Register
31
4
3
2
1
0
Rsvd
XIP7
XIP6
XIP5
XIP4
R, +0
R, +0
RW, +0
RW, +0
RW, +0