T89C51RD2-3CWC-M datasheet(46/86 Pages) ATMEL

46 / 86 page

Rev. F - 15 February, 2001

T89C51RD2

6.12. 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 24. 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.

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.

XRS1

XRS1 bit

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

XRS0

XRS0 bit

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

EXTRAM

EXTRAM bit

See Table 6.

ALE Output bit

Clear to restore ALE operation during internal fetches.

Set to disable ALE operation during internal fetches.

T89C51RD2-3CWC-M Datasheet(PDF) 46 Page - ATMEL Corporation