1.9.1 SMBus Timing Diagrams

1.10 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 ma-

chine resets to the SMBus idle state if either SMBData

or SMBCLK are held low for more than 35ms (t

Note that according to SMBus specification 2.0 all de-

vices are to timeout when either the SMBCLK or SMB-

Data 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 communi-

cation. After the start the LM90 will expect an SMBus

Address address byte.

1.11 DIGITAL FILTER

In order to suppress erroneous remote temperature readings

due to noise, the LM90 incorporates a user-configured digital

filter. The filter is accessed in the FILTER and ALERT CON-

FIGURE REGISTER at BFh. The filter can be set according

to the following table.

20033710

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

20033711

(b) Serial Bus Write to the Internal Command Register

20033712

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

FIGURE 7. SMBus Timing Diagrams

www.national.com

11