Broadcom BCM5722 - Figure 13: Two Masters Arbitrate for Smbus; Figure 14: Master Stops Transaction after Slave Naks

Programmer’s Guide BCM5722
10/15/07
Broadcom Corporation
Document 5722-PG101-R System Management Bus Page 30
Figure 13: Two Masters Arbitrate for SMBus
Figure 14: Master Stops Transaction After Slave NAKs
Depending on the type of transaction, the master sources the data byte on the SMBDATA lines:
• Write transactions—The master sources the data byte and the slave sinks/latches the data. The slave must ACK/NAK
write transactions.
• Read transactions—The slave sources the data byte and the master sinks/latches the data. The master must ACK/NAK
read transactions. Also, the master must drive the stop delimiter, which releases the SMBus and terminates the
transaction.
SMBDATA
(MASTER1)
SMBCLK
SMBDATA Float High by Master1
START
SMBDATA Sampled Low by Master1
(Master1 backs off SMBus)
S
MBDATA
(MASTER2)
Both Masters Sample SMBDATA High
(Both Masters Continue)
Master1 Quiesces—Arbitration Los
s
Master2 Continues Transaction
SMBDATA
SMBCLK
Slave Device NAK
(
Sampled High by Master)
SMBCLK Sampled High
STOP
SMBDATA Low to High Transitio
n