AT89C5131A-RDTIL datasheet(158/184 Pages) ATMEL

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AT89C5131A-L

4338F–USB–08/07

Reduced EMI Mode

The ALE signal is used to demultiplex address and data buses on port 0 when used with

external program or data memory. Nevertheless, during internal code execution, ALE

signal is still generated. In order to reduce EMI, ALE signal can be disabled by setting

AO bit.

The AO bit is located in AUXR register at bit location 0. As soon as AO is set, ALE is no

longer output but remains active during MOVX and MOVC instructions and external

fetches. During ALE disabling, ALE pin is weakly pulled high.

Table 112. AUXR Register

AUXR - Auxiliary Register (8Eh)

Reset Value = 0X0X 1100b

Not bit addressable

DPU

XRS1

XRS0

EXTRAM

Bit

Number

Bit

Mnemonic

Description

DPU

Disable Weak Pull Up

Cleared to enabled weak pull up on standard Ports

Set to disable weak pull up on standard Ports

Reserved

The value read from this bit is indeterminate. Do not set this bit.

Pulse length

Cleared to stretch MOVX control: the RD and the WR pulse length is 6 clock

periods (default).

Set to stretch MOVX control: the RD and the WR pulse length is 30 clock periods.

Reserved

The value read from this bit is indeterminate. Do not set this bit.

XRS1

ERAM Size

XRS1

XRS0

ERAM size

256 bytes

512 bytes

768 bytes

1024 bytes (default)

XRS0

EXTRAM

EXTRAM bit

Cleared to access internal ERAM using MOVX at Ri at DPTR.

Set to access external memory.

ALE Output bit

Cleared, ALE is emitted at a constant rate of 1/6 the oscillator frequency (or 1/3 if

X2 mode is used) (default).

Set, ALE is active only during a MOVX or MOVC instruction is used.

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