LM90

SNIS126A – MAY 2004 – REVISED MARCH 2013

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SMBus Timing Diagrams

Figure 8. (a) Serial Bus Write to the internal Command Register followed by a the Data Byte

Figure 9. (b) Serial Bus Write to the Internal Command Register

Figure 10. (c) Serial Bus Read from a Register with the Internal Command Register preset to desired

value

SERIAL INTERFACE RESET

In the event that the SMBus Master is RESET while the LM90 is transmitting on the SMBData line, the LM90

must be returned to a known state in the communication protocol. This may be done in one of two ways:

1. When SMBData is LOW, the LM90 SMBus state machine resets to the SMBus idle state if either SMBData

devices are to timeout when either the SMBCLK or SMBData lines are held low for 25-35ms. Therefore, to

insure a timeout of all devices on the bus the SMBCLK or SMBData lines must be held low for at least 35ms.

2. When SMBData is HIGH, have the master initiate an SMBus start. The LM90 will respond properly to an

SMBus start condition at any point during the communication. After the start the LM90 will expect an SMBus

Address address byte.

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