mg84fl54b Megawin Technology, mg84fl54b Datasheet - Page 31

• Manufacturer Part Number: mg84fl54b
• Description: Full-speed Usb Micro-controller
• Manufacturer: Megawin Technology

Broadcast 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 SADDR are to be used and which bits are “don’t care”. The SADEN
mask can be logically ANDed with the SADDR 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 recognized while
excluding others.
The following examples will help to show the versatility of this scheme:
Slave 0
Slave 1
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
Slave 1
Slave 2
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 trended 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 leaded 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.
MEGAWIN
SADDR = 1100 0000
SADEN = 1111 1101
Given = 1100 00X0
SADDR = 1100 0000
SADEN = 1111 1110
Given = 1100 000X
SADDR = 1100 0000
SADEN = 1111 1001
Given = 1100 0XX0
SADDR = 1110 0000
SADEN = 1111 1010
Given = 1110 0X0X
SADDR = 1110 0000
SADEN = 1111 1100
Given = 1110 00XX
MG84FL54B Data sheet
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