Datasheet
DS2480B
Maxim Integrated ........................................................................................................................................................................................... 17
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
8µs 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 22µs*. 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.