DS32EL0421, DS32ELX0421

SNLS282F – MAY 2008 – REVISED APRIL 2013

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6. The Host drive the 8-bit data byte.

7. The Device drives an ACK bit (“0”).

8. The Host drives a STOP condition.

9. The Host de-selects the device by driving its SMBus CS signal Low.

The WRITE transaction is completed, the bus goes IDLE and communication with other SMBus devices may

now occur.

Reading a Register

To read a register, the following protocol is used (see SMBus 2.0 specification).

1. The Host (Master) selects the device by driving its SMBus Chip Select (SMB_CS) signal HIGH.

2. The Host drives a START condition, the 7-bit SMBus address, and a “0” indicating a WRITE.

3. The Device (Slave) drives the ACK bit (“0”).

4. The Host drives the 8-bit Register Address.

5. The Device drives an ACK bit (“0”).

6. The Host drives a START condition.

7. The Host drives the 7-bit SMBus Address, and a “1” indicating a READ.

8. The Device drives an ACK bit “0”.

9. The Device drives the 8-bit data value (register contents).

10. The Host drives a NACK bit “1”indicating end of the READ transfer.

11. The Host drives a STOP condition.

12. The Host de-selects the device by driving its SMBus CS signal Low.

The READ transaction is completed, the bus goes IDLE and communication with other SMBus devices may now

occur.

SMBus Configurations

Many different configurations of the SMBus are possible and depend upon the specific requirements of the

applications. Several possible applications are described.

Configuration 1

The deserializer SMB_CS may be tied High (always enabled) since it is the only device on the SMBus. See

Figure 8.

Configuration 2

Since the multiple SER devices have the same address, the use of the individual SMB_CS signals is required.

To communicate with a specific device, its SMB_CS is driven High to select the device. After the transaction is

complete, its SMB_CS is driven Low to disable its SMB interface. Other devices on the bus may now be selected

with their respective chip select signals and communicated with. See Figure 9.

Configuration 3

The addressing field is limited to 7-bits by the SMBus protocol. Thus it is possible that multiple devices may

share the same 7-bit address. An optional feature in the SMBus 2.0 specification supports an Address Resolution

Protocol (ARP). This optional feature is not supported by the DS32EL0421/DS32ELX0421 devices. Solutions for

this include: the use of the independent SMB_CS signals, independent SMBus segments, or other means.

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