XRT79L71IB datasheet(9/109 Pages) EXAR

9 / 109 page

XRT79L71

REV. 1.0.0

1-CHANNEL DS3/E3 ATM UNI/PPP/CLEAR-CHANNEL FRAMER IC - HARDWARE

A16

ALE/AS

Address Latch Enable/Address Strobe:

The exact function of this input pin depends upon which mode the Microprocessor

Interface has been configured to operate in.

Intel-Asynchronous Mode - ALE

If the Microprocessor Interface of the XRT79L71 has been configured to operate in

the Intel-Asynchronous Mode, then this active-"High" input pin is used to latch the

address (present at the Microprocessor Interface Address Bus pins (A[14:0]) into the

XRT79L71 Microprocessor Interface block and to indicate the start of a READ or

WRITE cycle.

Pulling this input pin "High" enables the input bus drivers for the Address Bus input

pins (A[14:0]). The contents of the Address Bus will be latched into the XRT79L71

Microprocessor Interface circuitry, upon the falling edge of this input signal.

Motorola-Asynchronous (68K) Mode - AS

If the Microprocessor Interface has been configured to operate in the Motorola-Asyn-

chronous Mode, then this active-"Low" input pin is used to latch the data (residing on

the Address Bus, A[14:0]) into the Microprocessor Interface circuitry of the

XRT79L71.

Pulling this input pin "Low" enables the input bus drivers for the Address Bus input

pins. The contents of the Address Bus will be latched into the Microprocessor Inter-

face circuitry, upon the rising edge of this signal.

Power PC 403 Mode - No Function - Tie to GND:

If the Microprocessor Interface has been configured to operate in the Power PC 403

Mode, then this input pin has no role nor function and should be tied to GND.

D14

Chip Select Input:

The user must assert this active "Low" signal in order to select the Microprocessor

Interface for READ and WRITE operations between the Microprocessor and the

XRT79L71 on-chip registers and buffer/memory locations.

D13

INT

Interrupt Request Output:

This active-"Low" output signal will be asserted when the XRT79L71 is requesting

interrupt service from the Microprocessor. This output pin should typically be con-

nected to the Interrupt Request input of the Microprocessor.

PIN DESCRIPTIONS

PIN #NAME

TYPE

DESCRIPTION

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