DS2480 Dallas Semiconducotr, DS2480 Datasheet - Page 9

• Manufacturer Part Number: DS2480
• Description: Serial 1.Wire Line Driver
• Manufacturer: Dallas Semiconducotr

To perform a Search ROM sequence one starts with all
bits r
response bits r’
deactivated. Thus, if r’
occurred during the search procedure and the last
sequence has to be repeated. Otherwise r’
is the ROM code of the device that has been found and
addressed.
For the next Search ROM sequence one re–uses the
previous set r
the index number of the highest discrepancy flag that is
1 and sets all r
until the highest discrepancy occurs in the same bit
position for two consecutive passes.
The table below shows an example for the communica-
tion between host and DS2480 to perform one pass
through the Search ROM function using the Search
Accelerator. After a device has been identified and
addressed, a (not specified here) memory function is
executed and finally a reset pulse is generated. This
example assumes that the DS2480 was in Command
Mode and that regular 1–Wire speed is used.
Search Accelerator Usage Example
Generate Reset Pulse
Set Data Mode
Search ROM command
Set Command Mode
Search Accelerator On
Set Data Mode
Send 16 bytes
Set Command Mode
Search Accelerator Off
Set Data Mode
Do Memory Function
Set Command Mode
Generate Reset Pulse
n
Action Sequence
being 0s. In case of a bus error, all subsequent
n
i
(n = 0 ... 63) but sets r
to 0 with i > m. This process is repeated
n
are 1’s until the Search Accelerator is
63
and d
63
are both 1, an error has
Host TX
data
m
C1
B1
A1
C1
E1
F0
E3
E1
E3
E1
E3
to 1 with “m” being
n
(n = 0 ... 63)
(nothing)
(nothing)
(nothing)
(nothing)
(nothing)
response
(nothing)
(nothing)
(nothing)
Host RX
(as sent)
C9
C9
CONFIGURATION COMMANDS
The DS2480 is designed to be configurable for the vary-
ing requirements of its application. When the device
powers up and/or performs a master reset cycle, the
hard–wired default configuration settings take effect.
These settings will work on a short 1–Wire bus and
assume regular 1–Wire communication speed. To
change these default settings and to verify the current
settings, the logic of the DS2480 supports configuration
commands. A summary of the available configuration
parameters, their default settings at regular and Over-
drive speed and their applicability is shown in Table 3.
Parameters not related to the communication speed on
the 1–Wire bus specify the duration of the 12V program-
ming pulse, the duration of the strong pull–up to 5V and
the baud rate on the interface that connects the DS2480
to the host. The remaining three parameters are used to
modify the 1–Wire communication wave forms if one
selects “Flexible Speed” (see “Communication Com-
mands” for speed selection).
Flexible speed is implemented to improve the perfor-
mance of large MicroLAN Networks. This is accom-
plished by:
The latter two functions are controlled by a single
parameter. Taking advantage of flexible speed requires
changing one or more of these parameters from their
default values. Otherwise the waveforms will be identi-
cal to those at regular speed.
Each configuration parameter is identified by its 3–bit
parameter code and can be programmed for one of a
maximum 8 different values using a 3–bit value code. A
matrix of parameter codes and value codes with the
associated physical values in shown in Table 4.
limiting the slew rate on falling edges (e. g., at the
beginning of time slots, to reduce ringing),
extending the Write 1 low time (allows the current flow
through the network to end slowly, to prevent voltage
spikes from inductive kickback),
delaying the time point when reading a bit from the
1–Wire bus (gives the network more time to stabilize,
to get a higher voltage margin) and
adding extra recovery time between Write 0 time slots
(allows more energy transfer through the network, to
replenish the parasite power supply of the devices on
the bus).
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DS2480