參數(shù)資料
型號(hào)： DS2407P
英文描述： Dual Addressable Switch Plus 1K.Bit Memory
中文描述： 雙尋址開關(guān)與1K.Bit記憶
文件頁(yè)數(shù)： 22/31頁(yè)
文件大?。?/td> 194K
代理商： DS2407P
DS2407
012099 22/31
Conditional Search ROM [ECh]
The Conditional Search ROM command operates simi-
larly to the Search ROM command except that only
devices fulfilling the specified condition will participate in
the search. The condition is specified by the bit func-
tions CSS0 to CSS4 in Status Memory location 7. The
power–on default settings of these bits are stored in
EPROM in Status Memory location 6. If this EPROM
byte is not programmed, all CSS bits will be 1s. The
Conditional Search ROM provides an efficient means
for the bus master to determine devices in a multidrop
system that have to signal a status change, e.g. the
opening of a window in a building control application.
After each pass of the Conditional Search that success-
fully determined the 64–bit ROM for a specific device on
the multidrop bus, that particular device can be individu-
ally accessed as if a Match ROM had been issued since
all other devices will have dropped out of the search pro-
cess and are waiting for a reset pulse.
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).
Figure 13 shows a table of all qualifying conditions and
the required settings for CSS0 to CSS4.
The activity latch (Figure 10) captures an event for
interrogation by the bus master at a later time. In this
way, the bus master needs not to poll devices continu-
ously. The activity latch is cleared to 0 when the device
powers up and is set to 1 with the first negative or posi-
tive edge detected on the associated PIO channel. The
activity latch can also be cleared by writing a 1 into bit 7
of the Channel Control Byte 1. When using the activity
latch the output transistor of the selected channel
should be non–conducting. Otherwise signals applied
to the PIO pin will be shorted to ground by the low imped-
ance of the output transistor.
The channel of interest is specified by the Channel
Select bits CSS3 and CSS4. The sampling of the source
within the selected channel will take place on comple-
tion of the Conditional Search command byte. The
Channel selection codes are as follows:
CSS4,
0
0
1
1
CSS3
0
1
0
1
Channel Selection
neither channel selected
channel A only
channel B only
channel A OR channel B
If both CSS3 and CSS4 are 1, the logical values of the
selected signal source of both channels are ORed and
the result is compared to specified polarity. If, for exam-
ple, the specified polarity is 0, the signal source of both
channels must be 0 to allow the device to respond to the
Conditional Search. If both CSS3 and CSS4 are 0 nei-
ther channel is selected. Under this condition the device
will always respond to the Conditional Search if the
polarity bit CSS0 is 0, disregarding the status of the
selected source. If neither channel is selected and
CSS0 = 1, the device will ignore the Conditional Search
but will respond to the regular Search ROM command.
The source selection for the Conditional Search is done
through the Source Select bits CSS1 and CSS2. The
codes for these bits are as follows:
CSS2,
0
0
1
1
CSS1
0
1
0
1
Source Selection
Hidden Mode
Activity Latch
channel flip flop
PIO Status
Setting both CSS1 and CSS2 to 0 will put the device into
a “Hidden Mode” where it keeps its status but only
responds to the Match ROM (always) and Conditional
Search command (only if the polarity bit CSS0 is set to
1). While in “Hidden Mode” the device will never give a
Presence Pulse. When powering up into the “Hidden
Mode”, i.e., when bits 1 and 2 of status byte 6 have been
programmed to 0, the device will give one Presence
Pulse for every power–up sequence. If the device is in
Hidden Mode and the polarity bit is set to 0, the device
will not participate in the Conditional Search. As long as
the device is not programmed to power–up into “Hidden
Mode” the “Hidden Mode” can always be ended by a
power–on reset. Otherwise the only way to get the
device out of “Hidden Mode” is by remembering and
matching its 64–bit registration number and setting
CSS1 or CSS2 to 1.
The Conditional Search Polarity is specified by CSS0. If
CSS0 is 0, the DS2407 will respond to a Conditional
Search command if the status of the selected source for
the specified channel is a logic 0. If CSS0 is set to 1, the
source level needs to be a logic 1.
For 1–channel versions of the DS2407 the channel B
input will always be a logic 0 level. CSS4 should not be
set to 1 therefore to avoid unwanted influence from
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