at89c5131 ATMEL Corporation, at89c5131 Datasheet - Page 154

• Manufacturer Part Number: at89c5131
• Description: 8-bit Flash Microcontroller With Full Speed Usb Device At89c5131
• Manufacturer: ATMEL Corporation

Reduced EMI Mode
152
AT89C5131
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 110. AUXR Register
AUXR - Auxiliary Register (8Eh)
Reset Value = 0X0X 1100b
Not bit addressable
Number
Bit
DPU
7
6
5
4
3
2
1
0
7
Mnemonic
EXTRAM
XRS1
XRS0
DPU
Bit
M0
AO
-
-
6
-
Description
Disable Weak Pull Up
Cleared to enabled weak pull up on standard Ports
Set to disable weak pull up on standard Ports
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.
Reserved
The value read from this bit is indeterminate. Do not set this bit.
ERAM Size
XRS1
0
0
1
1
EXTRAM bit
Cleared to access internal ERAM using MOVX at Ri at DPTR.
Set to access external memory.
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.
M0
5
XRS0 ERAM size
0
1
0
1
256 bytes
512 bytes
768 bytes
1024 bytes (default)
4
-
XRS1
3
XRS0
2
EXTRAM
1
4136C–USB–04/05
AO
0