DS2406

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Conditional Search ROM [ECh]

The Conditional Search ROM command operates similarly to the Search ROM command except that only

devices fulfilling the specified condition will participate in the search. This command provides an

efficient means for the bus master to identify devices in a multidrop system that have to signal a status

change, e.g. the opening of a window in a building control application.

The condition is specified by the bit functions CSS0 to CSS4 in Status Memory location 7. At power-on

all these bits are 1s. They can be changed by means of the Write Status command. As long as the device

remains powered up, the modified search conditions are available for use at any time. For the conditional

search, one can specify the polarity (HIGH or LOW; CSS0), the source (PIO-pin, channel flip flop or

activity latch; CSS1, CSS2) and the channel of interest (A, B or the logical OR of A, B; CSS3, CSS4).

Table 2 shows all qualifying conditions and the required settings for CSS0 to CSS4.

QUALIFYING CONDITIONS FOR CONDITIONAL SEARCH Table 2

DESCRIPTION

CONDITIONAL SEARCH SELECT CODE

CHANNEL SELECT

SOURCE SELECT

POLARITY

CONDITION

CHANNEL

CSS4

CSS3

CSS2

CSS1

CSS0

RESERVED

Don’t care

0

0

0/1

Unconditional

neither one

0

0

At least one of these

bits needs to be 1

0

Activity Latch = 0

A

0101

0

Activity Latch = 1

A

0101

1

Channel FF = 0

(transistor on)

A

0110

0

Channel FF = 1

(transistor off)

A

0110

1

PIO Low

A

0111

0

PIO High

A

0111

1

Activity Latch = 0

B

1001

0

Activity Latch = 1

B

1001

1

Channel FF = 0

(transistor on)

B

1010

0

Channel FF = 1

(transistor off)

B

1010

1

PIO Low

B

1011

0

PIO High

B

1011

1

Activity Latch = 0

A or B

1101

0

Activity Latch = 1

A or B

1101

1

Channel FF = 0

(transistor on)

A or B

1110

0

Channel FF = 1

(transistor off)

A or B

1110

1

PIO Low

A or B

1111

0

PIO High

A or B

1111

1