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MX10EXA View Datasheet(PDF) - Macronix International

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MX10EXA
Automatic Address Recognition
Automatic Address Recognition is a feature which al-
lows the UART to recognize certain addresses in the
serial bit stream by using hardware to make the com-
parisons. This feature saves a great deal of software
overhead by eliminating the need for the software to ex-
amine every serial address which passes by the serial
port. This feature is enabled by setting the SM2 bit in
SCON. In the 9 bit UART modes, mode 2 and mode 3,
the Receive Interrupt flag (RI) will be automatically set
when the received byte contains either the "Given"” ad-
dress or the “Broadcast” address. The 9 bit mode re-
quires that the 9th information bit is a 1 to indicate that
the received information is an address and not data.
Automatic address recognition is shown in Figure 18.
Using the Automatic Address Recognition feature allows
a master to selectively communicate with one or more
slaves by invoking the Given slave address or addresses.
All of the slaves may be contacted by using the Broad-
cast address. Two special Function Registers are used
to define the slave’s address, SADDR, and the address
mask, SADEN. SADEN is used to define which bits in
the SAD DR are to be used and which bits are “don’t
care”. The SADEN mask can be logically ANDed with
the SAD DR to create the “Given” address which the
master will use for addressing each of the slaves. Use
of the Given address allows multiple slaves to be recog-
nized while excluding others. The following examples will
help to show the versatility of this scheme:
Siave0
Slavel
SADDR
SADEN
Given
SADDR
SADEN
Given
=1100
=1111
=1100
=1100
=1111
=1100
0000
1101
00X0
0000
1110
000X
In the above example SADDR is the same and the SAD
EN data is used to differentiate between the two slaves.
Slave 0 requires a 0 in bit 0 and it ignores bit 1. Slave 1
requires a 0 in bit 1 and bit 0 is ignored. A unique ad-
dress for Slave 0 would be 1100 0010 since slave 1
requires a 0 in bit 1. A unique address for slave 1 would
be 1100 0001 since a 1 in bit 0 will exclude slave 0. Both
slaves can be selected at the same time by an address
which has bit 0 = 0 (for slave 0) and bit 1 = 0 (for slave
1). Thus, both could be addressed with 1100 0000.
In a more complex system the following could be used
to select slaves 1 and 2 while excluding slave 0:
Slave0
Slave 1
SIave2
SADDR
SADEN
Given
SADDR
SADEN
Given
SADDR
SADEN
Given
=1100
=1111
=1100
=1110
=1111
=1110
=1110
=1111
=1110
0000
1001
0XX0
0000
1010
0X0X
0000
1100
00XX
In the above example the differentiation among the 3
slaves is in the lower 3 address bits. Slave 0 requires
that bit 0 = 0 and it can be uniquely addressed by 1110
0110. Slave 1 requires that bit 1 = 0 and it can be uniquely
addressed by 1110 and 0101. Slave 2 requires that bit 2
= 0 and its unique address is 1110 0011. To select Slaves
0 and 1 and exclude Slave 2 use address 1110 0100,
since it is necessary to make bit 2 = 1 to exclude slave
2.
The Broadcast Address for each slave is created by tak-
ing the logical OR of SADDR and SADEN. Zeros in this
result are tested as don’t-cares. In most cases, inter-
preting the don’t-cares as ones, the broadcast address
will be FF hexadecimal.
Upon reset SADDR and SADEN are loaded with Os. This
produces a given address of all “don’t cares” as well as
a Broadcast address of all “don’t cares”. This effec-
tively disables the Automatic Addressing mode and al-
lows the microcontroller to use standard UART drivers
which do not make use of this feature.
P/N:PM0625 Specifications subject to change without notice, contact your sales representatives for the most update information. REV. 1.0, JUL. 01, 2005
36
 

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