AT89LP51RD2 Atmel Corporation, AT89LP51RD2 Datasheet - Page 117

• Manufacturer Part Number: AT89LP51RD2
• Manufacturer: Atmel Corporation

Specifications of AT89LP51RD2

• Flash (kbytes): 64 Kbytes
• Max. Operating Frequency: 20 MHz
• Cpu: 8051-1C
• Max I/o Pins: 42
• Spi: 1
• Twi (i2c): 1
• Uart: 1
• Adc Channels: 7
• Adc Resolution (bits): 10
• Adc Speed (ksps): 153.8
• Sram (kbytes): 2.25
• Self Program Memory: API
• Operating Voltage (vcc): 2.4 to 5.5
• Timers: 4
• Isp: SPI/OCD/UART
• Watchdog: Yes

17.4.1
3714A–MICRO–7/11
Given Address
Two special Function Registers are used to define the slave’s address, SADDR (A9H), and the
address mask, SADEN (B9H). 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 show the versatility of this scheme:
Slave 0
Slave 1
In the previous 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 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.
Upon reset the SADDR and SADEN registers are loaded with “0”s. 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 microcontroller to use standard 80C51-
type UART drivers which do not make use of this feature.
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
AT89LP51RD2/ED2/ID2 Preliminary
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