T89C51RD2-RDTIL datasheet(49/104 Pages) ATMEL

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T89C51RD2

4243G–8051–05/03

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 31. AUXR Register

AUXR - Auxiliary Register (8Eh)

Reset Value = XX0X 1000b

Not bit addressable

XRS1

XRS0

EXTRAM

Bit

Number

Bit

Mnemonic

Description

Reserved

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

Reserved

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

5M0

M0 bit: Pulse length in clock period

Stretch MOVX control: the RD/ and the WR/ pulse length is increased

according to the value of M0. see table 6

Reserved

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

3XRS1

XRS1 bit

XRAM size: Accessible size of the XRAM. See Table 6.

2XRS0

XRS0 bit

XRAM size: Accessible size of the XRAM. Table 6.

1EXTRAM

EXTRAM bit

See Table 6.

0AO

ALE Output bit

Clear to restore ALE operation during internal fetches.

Set to disable ALE operation during internal fetches.

T89C51RD2-RDTIL Datasheet(PDF) 49 Page - ATMEL Corporation

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