AT89S8253 Atmel Corporation, AT89S8253 Datasheet - Page 21

• Manufacturer Part Number: AT89S8253
• Manufacturer: Atmel Corporation

Specifications of AT89S8253

• Flash (kbytes): 12 Kbytes
• Max. Operating Frequency: 24 MHz
• Cpu: 8051-12C
• Max I/o Pins: 32
• Spi: 1
• Uart: 1
• Sram (kbytes): 0.25
• Eeprom (bytes): 2048
• Operating Voltage (vcc): 2.7 to 5.5
• Timers: 3
• Isp: SPI
• Watchdog: Yes

3286P–MICRO–3/10
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 previous 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 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 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 microcontroller
to use standard 80C51-type UART drivers which do not make use of this feature.
SADDR = 1100 0000
SADEN = 1111 1001
Given
SADDR = 1110 0000
SADEN = 1111 1010
Given
SADDR = 1110 0000
SADEN = 1111 1100
Given
= 1100 0XX0
= 1110 0X0X
= 1110 00XX
AT89S8253
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