DS28E10 Просмотр технического описания (PDF) - Maxim Integrated

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DS28E10

1-Wire SHA-1 Authenticator

Maxim Integrated 

ABRIDGED DATA SHEET

1-Wire SHA-1 Authenticator

1-Wire Bus System

The 1-Wire bus is a system that has a single bus master

and one or more slaves. In all instances the DS28E10

is a slave device. The bus master is typically a micro-

controller. The discussion of this bus system is broken

down into three topics: hardware configuration, transac-

tion sequence, and 1-Wire signaling (signal types and

timing). The 1-Wire protocol defines bus transactions in

terms of the bus state during specific time slots, which

are initiated on the falling edge of sync pulses from the

bus master.

Hardware Configuration

The 1-Wire bus has only a single line by definition; it is

important that each device on the bus be able to drive

it at the appropriate time. To facilitate this, each device

attached to the 1-Wire bus must have open-drain or

three-state outputs. The 1-Wire port of the DS28E10

is open drain with an internal circuit equivalent to that

shown in Figure 7.

A multidrop bus consists of a 1-Wire bus with multiple

slaves attached. The DS28E10 supports both a standard

and overdrive communication speed of 15.4kbps (max)

and 125kbps (max), respectively. The value of the pullup

resistor primarily depends on the network size and load

conditions. The DS28E10 requires a pullup resistor of

2.2kI (max) at any speed.

The idle state for the 1-Wire bus is high. If for any reason

a transaction must be suspended, the bus must be left

in the idle state if the transaction is to resume. If this

does not occur and the bus is left low for more than 16Fs

(overdrive speed) or more than 120Fs (standard speed),

one or more devices on the bus could be reset.

Transaction Sequence

The protocol for accessing the DS28E10 through the

1-Wire port is as follows:

• Initialization

• ROM Function Command

• Memory/SHA-1 Function Command

• Transaction/Data

Initialization

All transactions on the 1-Wire bus begin with an initializa-

tion sequence. The initialization sequence consists of a

reset pulse transmitted by the bus master followed by a

presence pulse(s) transmitted by the slave(s). The pres-

ence pulse lets the bus master know that the DS28E10

is on the bus and is ready to operate. For more details,

see the 1-Wire Signaling section.

1-Wire ROM Function Commands

Once the bus master has detected a presence, it can

issue one of the seven ROM function commands that

the DS28E10 supports. All ROM function commands are

8 bits long. A list of these commands follows (see the

flowchart in Figure 8). Under certain conditions, the ROM

function commands may not operate properly right after

power-up. See the Applications Information section for a

method to ensure proper operation.

Read ROM [33h]

The Read ROM command allows the bus master to read

the DS28E10’s 8-bit family code, unique 48-bit serial

number, and 8-bit CRC. This command can only be used

if there is a single slave on the bus. If more than one

slave is present on the bus, a data collision occurs when

BUS MASTER

Rx

Tx

OPEN-DRAIN

PORT PIN

VPUP

RPUP

Rx = RECEIVE

Tx = TRANSMIT

DS28E10 1-Wire PORT

DATA

Rx

IL

Tx

100Ω MOSFET

Figure 7. Hardware Configuration

13

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