AT89C51RC2-3CSCM 데이터 시트보기 (PDF) - Atmel Corporation
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AT89C51RC2-3CSCM Datasheet PDF : 127 Pages
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AT89C51RB2/RC2
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 64. AUXR Register
AUXR - Auxiliary Register (8Eh)
7
6
5
4
DPU
-
M0
-
3
XRS1
2
1
0
XRS0
EXTRAM
AO
Bit
Bit
Number Mnemonic Description
Disable Weak Pull-up
7
DPU Cleared to activate the permanent weak pull up when latch data is logic 1
Set to disactive the weak pull-up.
Reserved
6
-
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
5
M0 periods (default).
Set to stretch MOVX control: the RD and the WR pulse length is 30 clock
periods.
Reserved
4
-
The value read from this bit is indeterminate. Do not set this bit.
3
XRS1 XRAM Size
XRS1 XRS0 XRAM size
0
0
256 Bytes (default)
2
XRS0 0
1
512 Bytes
1
0
768 Bytes
1
1
1024 Bytes
EXTRAM Bit
Cleared to access internal XRAM using movx @ Ri @ DPTR.
1
EXTRAM Set to access external memory.
Programmed by hardware after Power-up regarding Hardware Security Byte
(HSB), default setting, XRAM selected.
ALE Output Bit
0
AO
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.
85
4180E–8051–10/06
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