CD1865 datasheet(38/150 Pages) INTEL

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CD1865 — Intelligent Eight-Channel Communications Controller

Datasheet

5.5.2

Method 1b — Full Interrupt – Type B, Three-Level

Interrupt with Single-Level Acknowledge

This method is illustrated in Figure 9. It is useful with 80X86 systems that use the 8259A Interrupt

Controller. Since the 8259A supplies its own vector to the host when an INTA cycle occurs, the

host can simply read the CD1865’s vector by the method described in the polled interface example

or a separate device select decode can be provided to drive the ACKIN* input.

After the 8259A supplies a vector to the 80X86 host CPU, the host performs a software

acknowledgment to the CD1865, and transfers the CD1865 vector to the host. This allows the

service request to be processed.

Figure 8. Three-Level Interrupt with Three-Level Acknowledge Example

EIGHT-LEVEL

PRIORITY

ENCODER

CD1865 # 2

CD1865 # 1

M68000

MICROPROCESSOR

ADDRESS

DECODE

LOGIC

A1–A3

A8–A23

A4–A7

D0–D7

AS*

IPL1

IPL2

IPL3

A0–A2

A3–A6

CS*

D0–D7

RREQ*

TREQ*

MREQ*

A0–A2

A3–A6

CS*

D0–D7

RREQ*

TREQ*

MREQ*

ACKIN*

ACKOUT*

ACKIN*

CD1865 Datasheet(PDF) 38 Page - Intel Corporation

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