ds2482-800 Maxim Integrated Products, Inc., ds2482-800 Datasheet - Page 6

• Manufacturer Part Number: ds2482-800
• Description: Eight-channel 1-wire Master
• Manufacturer: Maxim Integrated Products, Inc.

Channel Selection Register
The content of the Channel Selection Register specifies which of the channels is selected and will be the target of
subsequent 1-Wire communication commands. The DS2482-800 supports eight 1-Wire communication channels
IO0 to IO7. Only one of these channels can be active/selected at any time. Once selected, a 1-Wire channel
remains selected until a different channel is selected through the Channel Select command or by initiating a
device reset. After a device reset (power-up cycle or initiated by the Device Reset command) the IO0 channel is
selected.
Configuration Register
The DS2482 supports allows three 1-Wire features that are enabled or selected through the Configuration Register.
These features are:
These features can be selected in any combination. They apply equally to all 1-Wire channels. While APU, PPM
and 1WS maintain their state, SPU returns to its inactive state as soon as the strong pullup has ended.
Configuration Register Bit Assignment
After a device reset (power-up cycle or initiated by the Device Reset command) the Configuration Register reads
00h. When writing to the Configuration Register, the new data is accepted only if the upper nibble (bits 7 to 4) is the
one's complement of the lower nibble (bits 3 to 0). When read, the upper nibble is always 0h.
Active Pullup (APU)
The APU bit controls whether an active pullup (controlled slew-rate transistor) or a passive pullup (R
will be used to drive a 1-Wire line from low to high. When APU = 0, active pullup is disabled (resistor mode). Active
Pullup should always be selected unless there is only a single slave on the 1-Wire line. The active pullup does
not apply to the rising edge of a presence pulse or a recovery after a short on the 1-Wire line.
The circuit that controls rising edges (Figure 2) operates as follows: At t1 the pulldown (from DS2482 or 1-Wire
slave) ends. From this point on the 1-Wire bus is pulled high through R
capacitive load of the 1-Wire line determine the slope. In case that active pullup is disabled (APU = 0), the resistive
pullup continues, as represented by the solid line. With active pullup enabled (APU = 1), when at t2 the voltage has
reached a level between V
slew rate, as represented by the dashed line. The active pullup continues until t
on the resistive pullup will continue.
Figure 2. Rising Edge Pullup
1WS
bit 7



Active Pullup (APU)
Strong Pullup (SPU)
1-Wire Speed (1WS)
SPU
bit 6
bit 5
1
V
V
V
0V
APU
bit 4
1-Wire bus is
discharged
IL1max
CC
IH1MIN
IL1MAX
and V
1WS
bit 3
APU = 1
IH1min
t
1
SPU
bit 2
, the DS2482 actively pulls the 1-Wire line high applying a controlled
t
2
bit 1
t
APUOT
0
6 of 23
APU
bit 0
t
3
APU = 0
WPU
internal to the DS2482. V
APUOT
is expired at t3. From that time
WPU
CC
resistor)
and the