Slave 0
SADDR = 1100 0000
Slave 1
SADDR = 1100 0000
SADEN = 1111 1101
Given = 1100 00X0
SADEN = 1111 1110
Given = 1100 000X
In the above example SADDR is the same and the SADEN 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
address 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:
Slave 0
SADDR = 1100 0000
Slave 1
SADDR = 1110 0000
Slave 2
SADDR = 1110 0000
SADEN = 1111 1001
Given = 1100 0XX0
SADEN = 1111 1010
Given = 1110 0X0X
SADEN = 1111 1100
Given = 1110 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 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 taking the logical OR of SADDR and SADEN. Zeros in this
result are treated as don’t-cares. In most cases, interpreting the don’t-cares as ones, the broadcast address will
be FF hexadecimal.
Upon reset SADDR (SFR address 0A9H) and SADEN (SFR address 0B9H) are loaded with 0s. This produces a
given address of all “don’t cares” as well as a Broadcast address of all “don’t cares”. This effectively disables the
Automatic Addressing mode and allows the micro-controller to use standard 80C51 type UART drivers which do
not make use of this feature.
Figure 12-6. UART Multiprocessor Communication, Auto Address Recognition
MEGAWIN
MPC82G516A Data Sheet
62
MEGAWIN [ MEGAWIN TECHNOLOGY CO., LTD ]
