P8044AH-R0117 datasheet(34/65 Pages) INNOVASIC

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IA8044/IA8344

Data Sheet

SDLC Communications Controller

March 30, 2010

IA211010112-04

http://www.Innovasic.com

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Page 34 of 65

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4.9

Interrupts

The IA8044/IA8344 provides five interrupt sources. There are two external interrupts accessible

through pins INT0 and INT1, edge or level sensitive (falling edge or low level). There are also

internal interrupts associated with Timer 0 and Timer 1 and an internal interrupt from the SIU.

4.9.1

External Interrupts

The choice between external interrupt level or transition activity is made by setting IT1 and IT0

bits in the SFR TCON. When the interrupt event happens, a corresponding Interrupt Control Bit is

set (IT0 or IT1). This control bit triggers an interrupt if the appropriate interrupt bit is enabled.

When the interrupt service routine is vectored, the corresponding control bit (IT0 or IT1) is

cleared, provided that the edge triggered mode was selected. If level mode is active, the external

requesting source controls flags IT0 or IT1 by the logic level on pins INT0 or INT1 (0 or 1).

4.9.2

Timer 0 and Timer 1 Interrupts

Timer 0 and 1 interrupts are generated by TF0 and TF1 flags, which are set by the rollover of

Timers 0 and 1, respectively. When an interrupt is generated, the flag that caused this interrupt is

cleared by the hardware if the CPU accessed the corresponding interrupt service vector. This can

be done only if this interrupt is enabled in the IE register.

4.9.3

Serial Interface Unit Interrupt

The SIU generates an interrupt when a frame is received or transmitted. No interrupts are

generated for a received frame with errors.

4.9.4

Interrupt Priority Level Structure

There are two priority levels in the IA8044/IA8344—any interrupt can be individually

programmed to a high or low priority level. Modifying the appropriate bits in the SFR IP can

accomplish this. A low-priority interrupt service routine will be interrupted by a high-priority

interrupt. However, the high-priority interrupt cannot be interrupted.

If two interrupts of the same priority level occur, an internal polling sequence determines which

will be processed first. This polling sequence is a second priority structure defined as follows:

IE0 1—highest

TF0 2

IE1 3

TF1 4

SIU—lowest

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