DS2406
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
RESERVED
Unconditional
CHANNEL
CSS4
CSS3
CSS2
CSS1
CSS0
0/1
0
Don’t care
0
0
neither one
0
0
At least one of these
bits needs to be 1
Activity Latch = 0
Activity Latch = 1
Channel FF = 0
(transistor on)
Channel FF = 1
(transistor off)
PIO Low
A
A
A
0
0
0
1
1
1
0
0
1
1
1
0
0
1
0
A
0
1
1
0
1
A
A
B
B
B
0
0
1
1
1
1
1
0
0
0
1
1
0
0
1
1
1
1
1
0
0
1
0
1
0
PIO High
Activity Latch = 0
Activity Latch = 1
Channel FF = 0
(transistor on)
Channel FF = 1
(transistor off)
PIO Low
B
1
0
1
0
1
B
B
1
1
1
1
1
0
0
1
1
1
1
1
0
0
1
1
1
1
1
0
0
1
0
1
0
PIO High
Activity Latch = 0
Activity Latch = 1
Channel FF = 0
(transistor on)
Channel FF = 1
(transistor off)
PIO Low
A or B
A or B
A or B
A or B
1
1
1
0
1
A or B
A or B
1
1
1
1
1
1
1
1
0
1
PIO High
21 of 31
DALLAS [ DALLAS SEMICONDUCTOR ]
