CD1865 datasheet(40/150 Pages) INTEL

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CD1865 — Intelligent Eight-Channel Communications Controller

Datasheet

5.5.4

Method 3b — Polled Interface

This method is illustrated in Figure 11. Polled operation can be used with any type of host CPU, or

it can be used in combination with interrupts to provide a mixed-mode system optimized for a

particular application. In a polled system, the host reads the Service Request Status register (SRSR)

within the CD1865 to determine whether there are any channels that need service. (Note that unlike

traditional UARTs, only one register needs to be read to determine if there are any channels in any

device that need attention, and this saves time).

If the host finds channels needing service, it acknowledges the required type by reading one of the

three Request Acknowledge registers. These provide a vector that can be used to jump directly to

the correct service routine. Processing from this point proceeds as in the case of interrupt-driven

operation. Note that the difference between this method and Method 2b lies in how the host system

becomes aware of the need to service the CD1865. In Method 2b a single interrupt starts the

process. In Method 3b the host polls periodically. The two methods can be combined — an

interrupt triggers the first service, but the host continues to poll until any other pending requests are

serviced.

Figure 10. Single-Level Interrupt with Single-Level Acknowledge Example

CD1865 # 1

CD1865 # 2

MICROPROCESSOR

ADDRESS

DECODE

LOGIC

A1–A3

A8–A23

A4–A7

D0–D7

ALE

INT

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) 40 Page - Intel Corporation

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