DS2482-100(2009) データシートの表示（PDF） - Maxim Integrated

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DS2482-100
(Rev.:2009)

Single-Channel 1-Wire Master

Maxim Integrated 

Single-Channel 1-Wire Master

Device Registers

The DS2482-100 has three registers that the I2C host

can read: Configuration, Status, and Read Data. These

registers are addressed by a read pointer. The position

of the read pointer, i.e., the register that the host reads

in a subsequent read access, is defined by the instruc-

tion the DS2482-100 executed last. To enable certain

1-Wire features, the host has read and write access to

the Configuration Register.

Configuration Register

The DS2482-100 supports three 1-Wire features that

are enabled or selected through the Configuration

Register. These features are:

• Active Pullup (APU)

• Strong Pullup (SPU)

• 1-Wire Speed (1WS)

These features can be selected in any combination.

While APU and 1WS maintain their state, SPU returns to

its inactive state as soon as the strong pullup has ended.

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.

BIT 7

1WS

BIT 6

SPU

BIT 5

1

BIT 4

APU

Active Pullup (APU)

The APU bit controls whether an active pullup (con-

trolled slew-rate transistor) or a passive pullup (RWPU

resistor) is 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) oper-

ates as follows: At t1, the pulldown (from DS2482-100

or 1-Wire slave) ends. From this point on, the 1-Wire

bus is pulled high through RWPU internal to the

DS2482-100. VCC and the 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), and when at t2 the voltage has

reached a level between VIL1(MAX) and VIH1(MIN), the

DS2482-100 actively pulls the 1-Wire line high, applying

a controlled slew rate as represented by the dashed

line. The active pullup continues until tAPUOT is expired

at t3. From that time on the resistive pullup continues.

See the Strong Pullup (SPU) section for a way to keep

the pullup transistor conducting beyond t3.

Configuration Register Bit Assignment

BIT 3

1WS

BIT 2

SPU

BIT 1

0

BIT 0

APU

VCC

VIH1(MIN)

APU = 1

APU = 0

VIL1(MAX)

0V

1-Wire BUS IS DISCHARGED

tAPUOT

t1

t2

t3

Figure 2. Rising Edge Pullup

6 _______________________________________________________________________________________

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