Datasheet
DS2480B
A Write-1 and Read Data time slot is comprised of the segments t
LOW1
, t
DSO
and t
HIGH
. During Write-1
time slots, after the Write-1 low time t
LOW1
is over, the DS2480B waits for the duration of the data sample
offset and then samples the voltage at the 1-Wire bus to read the response. After this, the waiting time
t
HIGH1
must expire before the time slot is complete. A Write-0 time slot only consists of the two segments
t
LOW0
and t
REC0
.
If the network is large or heavily loaded, one should select flexible speed and extend t
LOW1
to more than
8s to allow the 1-Wire bus to completely discharge. Since a large or heavily loaded network needs more
time to recharge, it is also recommended to delay sampling the bus for reading. A higher value for t
DSO
will increase the voltage margin and also provide extra energy to the slave devices when generating a
long series of write 0 time slots. However, the total of t
LOW1
+ t
DSO
should not exceed 22s*. Otherwise
the slave device responding may have stopped pulling the bus low when transmitting a logic 0.
The idle time between time slots within a byte or during a 12-bit sequence while the Search Accelerator is
on is 0. Between bytes, 12-bit search sequences and single bits the idle time depends on the RS232 data
rate and the host’s response time. The response byte is sent to the host as soon as the last time slot of a
byte, 12-bit sequence or the command is completed.
Figure 6b. WRITE-1 AND READ DATA TIME SLOT
Speed t
LOW1
t
DSO
t
HIGH1
t
SLOT
*
Standard 8µs 3µs 49µs 60µs
Overdrive 1µs 1µs 8µs 10µs
Flexible 8µs to 15µs 3µs to 10µs 49µs 60µs to 74µs
Figure 6c. WRITE-0 TIME SLOT
Speed t
LOW0
t
REC0
t
SLOT
*
Standard 57µs 3µs 60µs
Overdrive 7µs 3µs 10µs
Flexible 57µs 3µs to 10µs 60µs to 67µs
*In a 5V environment (1V, full temperature range) the tolerance of the internal time base of 1-Wire
slave devices is much narrower than what it is when operated at the minimum voltage of 2.8V. Therefore,
the timing generated by the DS2480B is in compliance with the requirements of all 1-Wire/iButton 1-
Wire devices.
17 of 32