DS2480 datasheet(21/26 Pages) DALLAS

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DS2480

042498 21/26

HARDWARE APPLICATION EXAMPLES

This section discusses five typical application scenarios

of the DS2480. When directly designed into a new prod-

uct, the device can be connected as shown in Figure

10a.

The circuit becomes more complex if a 1–Wire bus is to

be interfaced to a port that provides and expects

inverted signals, but does not necessarily meet the

RS232C (

± 12V) standard (Figure 10b).

UART DIRECT Figure 10a

START

1–WIRE BUS

RETURN

VDD

VPP

RXD

TXD

POL

1–W

GND

UART

µC

SIN (RXD)

SOUT (TXD)

12V

(5V)

STOP

DS2480

+/(–) 5V RS232 Figure 10b

START

1–WIRE BUS

RETURN

VDD

VPP

RXD

TXD

POL

1–W

GND

UART

µC

(5V)

STOP

DTR

VOLTAGE

REGULATOR

DS2480

12V

RTS

RXD

TXD

GND

SEE TEXT

POWER

STEALING

DRIVER/

LEVEL SHIFTER

The signals DTR and RTS provide the power to operate

the DS2480. The resistor in the TXD line and the

Schottky diode limit the negative voltage at the TXD pin

of the DS2480 to 0.3V maximum. The resistor is typi-

cally 4.7 k

Ω. If the inverting driver is current–limited to 1

mA the resistor is not required.

From the DS2480’s perspective, this circuit will work

with inverted signals of

± 5V as well as 0 to 5V. Depend-

ing on the voltage levels the host expects, it may be nec-

essary to generate a negative voltage on the RXD line.

Figure 10c shows how this can be accomplished for a

true RS232C system.

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