Environmental Monitoring and Control Device
Datasheet
The Write Byte, Read Byte, Send Byte, and Receive Byte protocols are the only valid SMBus protocols for
the Device. This part responds to other protocols as described in the Invalid Protocol Section. Reference
the System Management Bus Specification, Rev 2.0.
The SMBus interface is used to read and write the registers in the Device. The register set is shown in
section Chapter 8 Register Set on page 37.
5.3
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 EMC device is 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 EMC device 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.
Note: Data bytes are transferred MSB first.
5.3.1 BYTE PROTOCOLS
When using the EMC SMBus Interface for byte transfers, 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 EMC device 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 EMC
device. 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 EMC register
with the SMBus Interface Address byte, followed by the data byte read from the EMC register 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 5.1 is performed correctly. Only one byte is transferred at time for a Write Byte protocol.
Table 5.1 -SMBus Write Byte Protocol
SLAVE
ADDR
REG.
FIELD: START
WR
ACK REG. ADDR ACK
ACK STOP
DATA
BITS:
1
7
1
1
8
1
8
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 5.2 is performed correctly. Only one byte is transferred at time for a Read Byte protocol.
SMSC EMC6D100/EMC6D101
Page 17
Rev. 09-09-04
DATASHEET
SMSC [ SMSC CORPORATION ]
