
The default power on SMBus address is 010110x binary, where x reflects the state defined by the A0 pin.  The 
A0/RESET#/THERM#/XNOR_OUT pin requires an external pullup resistor if the RESET# or THERM# functions are 
used.  This limits the SMBus address to 0101101 unless external circuitry is used to override the pull-up at power-up. 
SMSC DS – LPC47M192 
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DATASHEET 
7.18.2.1 
The Hardware Monitor Block SMBus implementation is a subset of the SMBus interface to the host.  The Hardware 
Monitor Block is a 
slave-only
 SMBus device. The implementation in the Hardware Monitor Block is a subset of 
SMBus since it only supports four protocols. 
The Read Byte, Receive Byte, Write Byte and Send Byte protocols are the only valid SMBus protocols for the 
Hardware Monitor Block. The part responds to other protocols as described in the Invalid Protocol Section. Reference 
the System Management Bus Specification, Rev 1.1. 
The SMBus interface is used to read and write the registers in the Hardware Monitor Block. The only valid registers 
for a read or write protocol are the registers shown in the Registers Section. 
SMBus Slave Interface 
7.18.2.1.1 Bus Protocols 
Typical Write Byte, Read Byte, Send Byte and Receive Byte protocols are shown below.  Register accesses are 
performed using 7-bit slave addressing, an 8-bit register address field, and an 8-bit data field.  The shading indicates 
the Hardware Monitor Block driving data on the SDA line; otherwise host data is on the SDA line. 
The slave address is the unique SMBus Interface Address for the Hardware Monitor Block that identifies it on SMBus. 
The register address field is the internal address of the register to be accessed. The register data field is the data that 
the host is attempting to write to the register or the contents of the register that the host is attempting to read. 
Data bytes are transferred MSB first. 
When using the Hardware Monitor Block SMBus Interface, a write will always consist of the SMBus Interface Address 
byte, followed by the Internal Address Register byte, then the data byte. There are two cases for a read: 
1. The normal read protocol consists of a write to the Hardware Monitor Block with the SMBus Interface Address 
byte, followed by the Internal Address Register byte. Then restart the Serial Communication with a Read consisting of 
the SMBus Interface Address byte, followed by the data byte read from the Hardware Monitor Block.  This can be 
accomplished by using the Read Byte protocol or by using the Send Byte protocol followed by the Receive Byte 
protocol. 
2. If the Internal Address Register is known to be at the desired Address, simply read the Hardware Monitor Block 
with the SMBus Interface Address byte, followed by the data byte read from the Hardware Monitor Block.  This 
corresponds to the Receive Byte protocol. 
Write Byte 
The Write Byte protocol is used to write data to the registers.  The data will only be written if the protocol shown in 
Table 1 is performed correctly.  Only one byte is transferred at time for a Write Byte protocol. 
Table 57 - SMBus Write Byte Protocol
FIELD: START 
SLAVE 
ADDR 
7 
WR
ACK 
REG. 
ADDR 
8 
ACK 
REG. 
DATA 
8 
ACK 
STOP 
Bits: 
1 
1 
1 
1 
1 
1 
Read Byte 
The Read Byte protocol is used to read data from the registers. The data will only be read if the protocol shown in 
Table 2 is performed correctly.  Only one byte is transferred at time for a Read Byte protocol.