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AT89C5131A-RDTIL 数据表(PDF) 158 Page - ATMEL Corporation |
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AT89C5131A-RDTIL 数据表(HTML) 158 Page - ATMEL Corporation |
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158 / 186 page  158 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 7 6 5 4 3 2 1 0 DPU - M0 - XRS1 XRS0 EXTRAM AO Bit Number Bit Mnemonic Description 7 DPU Disable Weak Pull Up Cleared to enabled weak pull up on standard Ports Set to disable weak pull up on standard Ports 6 - Reserved The value read from this bit is indeterminate. Do not set this bit. 5 M0 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. 4 - Reserved The value read from this bit is indeterminate. Do not set this bit. 3 XRS1 ERAM Size XRS1 XRS0 ERAM size 0 0 256 bytes 0 1 512 bytes 1 0 768 bytes 1 1 1024 bytes (default) 2 XRS0 1 EXTRAM EXTRAM bit Cleared to access internal ERAM using MOVX at Ri at DPTR. Set to access external memory. 0 AO 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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