DS2482-800 Просмотр технического описания (PDF) - Dallas Semiconductor -> Maxim Integrated

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DS2482-800

Eight-Channel 1-Wire Master

Dallas Semiconductor -> Maxim Integrated 

DS2482-800: Eight-Channel 1-Wire Master

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 four 1-Wire features that are enabled or selected through the Configuration Register.

These features are:

§ Active Pullup (APU)

§ Presence Pulse Masking (PPM)

§ Strong Pullup (SPU)

§ 1-Wire Speed (1WS)

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

bit 7

1WS

bit 6

SPU

bit 5

PPM

bit 4

APU

bit 3

1WS

bit 2

SPU

bit 1

PPM

bit 0

APU

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 (RWPU resistor)

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 be selected if the 1-Wire line has a substantial length (30 meters or more) or if there is a large

number (~20 or more) of devices connected to a 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 RWPU internal to the DS2482. 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), when at t2 the voltage has

reached a level between VIL1max and VIH1min, the DS2482 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 will continue.

Figure 2. Rising Edge Pullup

VCC

VIH1MIN

APU = 1

APU = 0

VIL1MAX

0V

1-Wire bus is

tAPUOT

discharged

t1

t2

t3

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