Rainbow Electronics T89C5121 - Manual (Page 83)

83
A/T8xC5121
4164G–SCR–07/06
To address a device by its individual address, the SADEN mask byte must be 1111
1111b .
For example:
SADDR0101 0110b
SADEN1111 1100b
Given0101 01XXb
The following is an example of how to use given addresses to address different slaves:
Slave A:SADDR1111 0001b
SADEN1111 1010b
Given1111 0X0Xb
Slave B:SADDR1111 0011b
SADEN1111 1001b
Given1111 0XX1b
Slave C:SADDR1111 0011b
SADEN1111 1101b
Given1111 00X1b
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 commu-
nicate 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 0; for slaves B and C, bit 1 is a don’t care bit. To communicate with
slaves A and B, but not slave C, 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 ).
Broadcast Address 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.:
SADDR0101 0110b
SADEN1111 1100b
SADDR OR SADEN1111 111Xb
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:
Slave A:SADDR1111 0001b
SADEN1111 1010b
Given1111 1X11b,
Slave B:SADDR1111 0011b
SADEN1111 1001b
Given1111 1X11B,
Slave C:SADDR = 1111 0010b
SADEN1111 1101b
Given1111 1111b
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.