Interrupt Control Unit
7-1
CHAPTER
7
INTERRUPT CONTROL UNIT
7.1
OVERVIEW
The Am186EM and Am188EM microcontrollers can receive interrupt requests from a
variety of sources, both internal and external. The internal interrupt controller arranges
these requests by priority and presents them one at a time to the CPU.
There are six external interrupt sources on the Am186EM and Am188EM microcontrollers—
five maskable interrupt pins (INT4–INT0) and the non-maskable interrupt (NMI) pin. There
are six internal interrupt sources that are not connected to external pins—three timers, two
DMA channels, and the asynchronous serial port.
The Am186EM and Am188EM microcontrollers provide three interrupts that are not present
on the 80C186 and 80C188 microcontrollers:
n
INT4, an additional external interrupt pin that operates like the INT3–INT0 pins
n
An internal watchdog timer interrupt
n
An internal interrupt from the serial port
The INT4–INT0 interrupt request pins can be used as direct interrupt requests. If more
inputs are needed, INT3–INT0 can also be cascaded with an 82C59A-compatible external
interrupt control device. An external interrupt controller can be used as the system master
by programming the internal interrupt controller to operate in slave mode. In all cases,
nesting can be enabled that allows high priority interrupts to interrupt lower-priority interrupt
service routines.
7.1.1
Definitions of Interrupt Terms
The following definitions cover some of the terminology that is used in describing the
functionality of the interrupt controller. Table 7-1 contains information regarding the
reserved interrupts.
7.1.1.1
Interrupt Type
An 8-bit interrupt type identifies each of the 256 possible interrupts.
Software exceptions, internal peripherals, and non-cascaded external interrupts supply the
interrupt type through the internal interrupt controller.
Cascaded external interrupts and slave-mode external interrupts get the interrupt type from
the external interrupt controller by means of interrupt acknowledge cycles on the bus.
Summary of Contents for AM186EM
Page 1: ...Am186 EM and Am188 EM Microcontrollers User s Manual...
Page 4: ...iv...
Page 12: ...Table of Contents xii...
Page 62: ...Peripheral Control Block 4 10...
Page 76: ...Chip Select Unit 5 14...
Page 122: ...Timer Control Unit 8 8...
Page 136: ...DMA Controller 9 14...
Page 144: ...Asynchronous Serial Port 10 8...
Page 158: ...Programmable I O Pins 12 6...
Page 186: ...Index I 12...