INTERRUPT CONTROL UNIT

Register Name:Interrupt Control Register (cascadable pins)

Register Mnemonic:

I0CON, I1CON

Register Function:Control register for the cascadable external interrupt pins

15

 

S

C

L

 

F

A

V

 

N

S

L

 

M

 

 

 

 

 

 

 

 

 

0

M

P

P

P

S

M

M

M

K

2

1

0

 

 

 

 

A1215-A0

Bit

Bit Name

Reset

Function

Mnemonic

State

 

 

 

 

 

 

SFNM

Special

0

Set to enable special fully nested mode.

 

Fully

 

 

 

Nested

 

 

 

Mode

 

 

 

 

 

 

CAS

Cascade

0

Set to enable cascade mode.

 

Mode

 

 

 

 

 

 

LVL

Level-trigger

0

Selects the interrupt triggering mode:

 

 

 

0 = edge triggering

 

 

 

1 = level triggering.

 

 

 

The LVL bit must be set when external 8259As

 

 

 

are cascaded into the Interrupt Control Unit.

 

 

 

 

MSK

Interrupt

1

Clear to enable interrupts from this source.

 

Mask

 

 

 

 

 

 

PM2:0

Priority

111

Defines the priority level for this source.

 

Level

 

 

 

 

 

 

NOTE: Reserved register bits are shown with gray shading. Reserved bits must be written to a logic zero to ensure compatibility with future Intel products.

Figure 8-6. Interrupt Control Register for Cascadable Interrupt Pins

8-15

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Intel 80C188XL, 80C186XL user manual Register NameInterrupt Control Register cascadable pins, I0CON, I1CON, Sfnm, Cas