DS2480 datasheet(3/26 Pages) DALLAS

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DS2480

042498 3/26

DS2480 BLOCK DIAGRAM Figure 1

MUX

CONFIGURATION

PROTOCOL

ANALYZER

PROTOCOL

ANALYZER

TIMING

GENERATOR

PROTOCOL

CONVERTER

1–WIRE

DRIVER

MS BIT OF SPEED CONTROL

(1 = RXD IS INVERTED)

VPP

1–W

RXD

POL

TXD

DEVICE OPERATION

The DS2480 can be described as a complex state

machine with two static and several dynamic states.

Two device–internal flags as well as functions assigned

to certain bit positions in the command codes determine

the behavior of the chip, as shown in the state transition

diagram (Figure 2). The DS2480 requires and gener-

ates a communication protocol of 8 data bits per charac-

ter, 1 stop bit and no parity. It is permissible to use two

stop bits on the TXD line. However, the DS2480 will only

assert a single stop bit on RXD.

When powering up, the DS2480 performs a master

reset cycle and enters the Command Mode, which is

one of the two static states. The device now expects to

receive one 1–Wire reset command on the TXD line

sent by the host at a data rate of 9600 bits per second

(see section Communication Commands for details).

This command byte is required solely for calibration of

the timing generator the DS2480 and is not translated

into any activity on the 1–Wire bus. After this first com-

mand byte the device is ready to receive and execute

any command as described later in this document.

A master reset cycle can also be generated by means of

software. This may be necessary if the host for any rea-

son has lost synchronization with the device. The

DS2480 will perform a master reset cycle equivalent to

the power–on reset if it detects start polarity in place of

the stop bit. The host has several options to generate

this condition. These include making the UART gener-

ate a break signal, sending a NULL character at a data

rate of 4800 bps and sending any character with parity

enabled and selecting space polarity for the parity bit.

As with the power–on reset, the DS2480 requires a

1–Wire reset command sent by the host at a data rate of

9600 bps for calibration.

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