LM40 datasheet(14/27 Pages) NSC

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1.0 Functional Description (Continued)

All devices (master or slave) must monitor the bus for an

Attention Request signal. The following notes clarify the

intended system operation that uses the Attention Request

Indication.

•

Masters are expected to use the attention request as a

trigger to read results from the LM40. This is done in a

sequence that covers all LM40s. This sequence is re-

ferred to as "master sensor read sequence".

•

After an Attention Request is sent by an LM40 until after

the next read from the Device Status register the LM40

does not send Attention Requests for a function event

since it is guaranteed that the master will read the Status

Note that the LM40 will send an attention for BER, re-

gardless of the Status register read, to help the master

with any error recovery operations and prevent dead-

locks.

•

A master must record the Attention Request event. It

must then scan all slave devices in the system by reading

their Device Status register and must handle any pending

event in them before it may assume that there are no

more events to handle.

Note: there is no indication of which slave has sent the

request. The requirement that multiple requests are not sent

allows the master to know within one scan of register reads

that there are no more pending events.

1.3.6 Fixed Device Number Setting

The LM40 device number is defined by strapping of the ADD

pin. The LM40 will wake (after Device Reset) with the Device

Number field of the Device Number register set to the ad-

dress as designated in Section 2.3 "Device Number". It is the

responsibility of the system designer to avoid having two

devices with the same Device Number on the bus.

Devices should be detected by the master by a read opera-

tion of the Device Number register. The read returns "000" if

there is no device at that address on the bus (the EP bit must

be ignored).

LM40 Arkusz danych(PDF) 14 Page - National Semiconductor (TI)