Rainbow Electronics T89C51RD2 - Manual (Page 46)

Rev. F - 15 February, 2001 46
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
7 6 5 4 3 2 1 0
- - M0 - XRS1 XRS0 EXTRAM AO
Bit
Number
Bit
Mnemonic
Description
7 -
Reserved
The value read from this bit is indeterminate. Do not set this bit.
6 -
Reserved
The value read from this bit is indeterminate. Do not set this bit.
5 M0
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
4 -
Reserved
The value read from this bit is indeterminate. Do not set this bit.
3 XRS1
XRS1 bit
XRAM size: Accessible size of the XRAM. See Table 6.
2 XRS0
XRS0 bit
XRAM size: Accessible size of the XRAM. Table 6.
1 EXTRAM
EXTRAM bit
See Table 6.
0 AO
ALE Output bit
Clear to restore ALE operation during internal fetches.
Set to disable ALE operation during internal fetches.