Datasheet

DS2408

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APPLICATION

The DS2408 is a multipurpose device. Typical applications include port expander for microcontrollers,

remote multichannel sensor/actuator, communication and control unit of a microterminal, or as network

interface of a microcontroller. Typical application circuits and communication examples are found later

in this data sheet (Figures 17 to 22).

OVERVIEW

Figure 1 shows the relationships between the major function blocks of the DS2408. The device has two

main data components: 1) 64-bit lasered ROM, and 2) 64-bit register page of control and status registers.

Figure 2 shows the hierarchical structure of the 1-Wire protocol. The bus master must first provide one of

the eight ROM function commands: 1) Read ROM, 2) Match ROM, 3) Search ROM, 4) Conditional

Search ROM, 5) Skip ROM, 6) Overdrive-Skip ROM, 7) Overdrive-Match ROM, or 8) Resume. Upon

completion of an Overdrive ROM command byte executed at standard speed, the device will enter

overdrive mode, where all subsequent communication occurs at a higher speed. The protocol required for

these ROM function commands is described in Figure 12. After a ROM function command is success-

fully executed, the control functions become accessible and the master may provide any one of the five

available commands. The protocol for these control commands is described in Figure 8. All data is read

and written least significant bit first.

Figure 1. DS2408 BLOCK DIAGRAM

64-BIT

LASERED ROM

CRC16

GENERATOR

PAGE

FUNCTION

CONTROL

1-WIRE

FUNCTION

CONTROL

PORT

FUNCTION

CONTROL

I/O

GND

PARASITE POWER

INTERNAL V

PORT

INTER-

FACE

RSTZ