AT80C51RD2 Atmel Corporation, AT80C51RD2 Datasheet - Page 36

• Manufacturer Part Number: AT80C51RD2
• Manufacturer: Atmel Corporation

Specifications of AT80C51RD2

• Max. Operating Frequency: 60 MHz
• Cpu: 8051-12C
• Max I/o Pins: 32
• Spi: 1
• Uart: 1
• Sram (kbytes): 1.25
• Operating Voltage (vcc): 2.7 to 5.5
• Timers: 4
• Watchdog: Yes

11.2.2
36
AT80C51RD2
Broadcast Address
The SADEN byte is selected so that each slave may be addressed separately.
For slave A, bit 0 (the LSB) is a don’t-care bit; for slaves B and C, bit 0 is a 1. To communicate
with slave A only, the master must send an address where bit 0 is clear (e.g. 1111 0000b).
For slave A, bit 1 is a 1; for slaves B and C, bit 1 is a don’t care bit. To communicate with slaves
B and C, but not slave A, the master must send an address with bits 0 and 1 both set (e.g. 1111
0011b).
To communicate with slaves A, B and C, the master must send an address with bit 0 set, bit 1
clear, and bit 2 clear (e.g. 1111 0001b).
A broadcast address is formed from the logical OR of the SADDR and SADEN registers with
zeros defined as don’t-care bits, e.g.:
The use of don’t-care bits provides flexibility in defining the broadcast address, however in most
applications, a broadcast address is FFh. The following is an example of using broadcast
addresses:
For slaves A and B, bit 2 is a don’t care bit; for slave C, bit 2 is set. To communicate with all of
the slaves, the master must send an address FFh. To communicate with slaves A and B, but not
slave C, the master can send and address FBh.
Slave C:SADDR1111 0010b
Slave A:SADDR1111 0001b
Slave B:SADDR1111 0011b
Slave C:SADDR
Broadcast
Given1111 0XX1b
SADEN1111 1101b
Given1111 00X1b
SADDR0101 0110b
SADEN1111 1100b
SADEN1111 1010b
Broadcast1111 1X11b,
SADEN1111 1001b
Broadcast1111 1X11B,
SADEN1111 1101b
Broadcast1111 1111b
= SADDR OR SADEN1111 111Xb
= 1111 0010b
4113D–8051–01/09