DS2409
DISCHARGE LINES [99h]
There may be situations where one has to force a power-on reset for parasitically powered 1-Wire devices
connected to the main or auxiliary output of the DS2409. For this purpose the Discharge Lines command
has been implemented. This command first deactivates the output lines and then turns on the pulldown
transistors of both, the main and the auxiliary outputs. This state will be maintained until the bus master
accesses the coupler again and issues a different control function command. The duration of the
discharge time should be 100 ms minimum and is controlled solely by the bus master.
Although any of the other control function commands will end the discharge cycle, it is recommended to
use the All Lines Off or Status Read/Write command to do so. This will allow the discharged lines to
fully recharge and prevent a sudden voltage droop on the active part of the network in case of a Direct-On
Main command. This precaution is not necessary with the Smart-On command.
DIRECT-ON MAIN [A5h]
The Direct-on Main command is typically used to activate the main 1-Wire output to subsequently issue a
reset pulse and access a device residing on the segment of the MicroLAN connected to the Main output of
the DS2409. If this command is received, the DS2409 will automatically set the auxiliary output to
inactive. Depending on the currently valid device status settings, the transistor at the control output may
change state (see Status Read/Write command).
SMART-ON MAIN [CCh]
When analyzing huge MicroLAN networks for changes in population it may be useful to limit the number
of devices participating in a Search ROM command. The smaller the number of participants, the faster
the responding devices are identified. The DS2409 supports the bus master in this process with the Smart-
On Main command. As a preparation for the subsequent steps, the first action of the Smart-On Main
command is deactivating the main output.
Compared to the Direct-On Main command, the Smart-On Main requires the bus master to follow the
function command with 16 more time slots. The first 8 time slots (reset stimulus) are translated by the
DS2409 as a reset low time on the Main 1-Wire output. Now the bus master reads the reset response byte.
This generates the reset high time where devices connected to the Main 1-Wire output may assert their
presence pulse. If a presence pulse was found, several of the most significant bits of the reset response
byte will be zeros. After these 16 time slots are completed the Main 1-Wire output will be activated (=
through-connected to the 1-Wire input of the DS2409). Now only the devices on the newly activated
segment of the MicroLAN are ready to receive a ROM function command optionally followed by a
memory function command. All other devices in the network will remain silent until the next reset pulse
is issued.
As with the Direct-On command, the Smart-On Main command will automatically set the auxiliary
output to inactive. Depending on the currently valid device status settings, the transistor at the control
output may change state (see Status Read/Write command). If the Smart-On Main command is terminated
by a 1-Wire reset pulse while receiving the reset stimulus, the DS2409 will immediately turn off the
pulldown transistor and let the output line go high.
SMART-ON AUXILIARY [33h]
This command works essentially the same way as the Smart-On Main command, but it affects the
auxiliary 1-Wire output. After the reset response byte is received by the bus master, the auxiliary output is
activated and the main output becomes inactive. Depending on the currently valid device status settings,
the transistor at the control output may change state (see Status Read/Write command).
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