at89c51re2-slsem ATMEL Corporation, at89c51re2-slsem Datasheet - Page 127

• Manufacturer Part Number: at89c51re2-slsem
• Description: At89c51re2 8-bit Flash Microcontroller
• Manufacturer: ATMEL Corporation

Reduced EMI Mode
110
AT89C51RE2
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 88. AUXR Register
AUXR - Auxiliary Register (8Eh)
Reset Value = XX00 10’HSB. XRAM’0b
Not bit addressable
Number
Bit
7
-
7
6
5
4
3
2
1
0
Mnemonic Description
EXTRAM
XRS2
XRS1
XRS0
Bit
M0
AO
6
-
-
-
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.
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.
XRAM Size
0 0 0 256 bytes
0 0 1 512 bytes
0 1 0 768 bytes(default)
0 1 1 1024 bytes
1 0 0 1792 bytes
EXTRAM bit
Cleared to access internal XRAM using movx @ Ri/ @ DPTR.
Set to access external memory.
Programmed by hardware after Power-up regarding Hardware Security Byte
(HSB), default setting, XRAM selected.
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.
XRS2 XRS1XRS0XRAM size
M0
5
XRS2
4
XRS1
3
XRS0
2
EXTRAM
1
7663B–8051–03/07
AO
0