DS1977-F5# Datasheet DS1977-F5# | P25-P27

DS1977

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VERIFY PASSWORD (SUCCESS)

RST PD Select VP TA Password Strong Pullup AA loop

VERIFY PASSWORD (FAIL ADDRESS OR PASSWORD)

RST PD Select VP TA Password Strong Pullup FF loop

READ VERSION (CANNOT FAIL)

RST PD Select RV 00h 00h Version Version FF loop

COMMUNICATION EXAMPLES

The examples in this section demonstrate the use of the memory functions in typical situations. The first example

shows how to read the ROM and the version register. In the second example, passwords are installed. The third

example shows how to write a couple of bytes and how to read adjacent memory pages.

EXAMPLE 1

Task: Read the ROM and the version register

With only a single DS1977 connected to the bus master, the communication is as follows:

MASTER MODE

DATA (LSB FIRST)

COMMENTS

TX (Reset) Reset Pulse

RX (Presence) Presence Pulse

TX 33h Issue Read ROM Command

RX <8 Bytes ROM ID> Read ROM ID

TX CCh Issue Read Version Register Command

TX 00h, 00h Write Two 00h Bytes

RX <Version>, <Version> Read Chip Version Code Twice

RX FFh Additional Reads Result in FFh Bytes

TX (Reset) Reset Pulse

RX (Presence) Presence pulse

EXAMPLE 2

Task: Install and activate passwords; passwords are currently not activated

This task is broken into the following steps:

1. Write new passwords to scratchpad

2. Read Scratchpad

3. Copy scratchpad

4. Verify new passwords

5. Activate password

DS1977

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With only a single DS1977 connected to the bus master, the communication is as follows:

MASTER MODE

DATA (LSB FIRST)

COMMENTS

Step 1 TX (Reset) Reset Pulse

RX (Presence) Presence Pulse

TX CCh Issue Skip ROM Command

TX 0Fh Issue Write Scratchpad Command

TX C0h

TA1, Target Address = C0h (Password Start

Address)

TX 7Fh TA2, Target Address = 7FC0h

TX <Read Password> Write 8-Byte Read Password to Scratchpad

TX <Full-Access Password>

Write 8-Byte Full-Access Password to

Scratchpad

TX (Reset) Reset Pulse

RX (Presence) Presence Pulse

Step 2 TX CCh Issue Skip ROM Command

TX AAh Issue Read Scratchpad Command

RX C0h Read TA1, Target Address = C0h

RX 7Fh Read TA2, Target Address = 7FC0h

RX 0Fh Read E/S-Byte

RX <16 Bytes>

Read Both Passwords from Scratchpad and

Compare to what was Written

TX (Reset) Reset Pulse

RX (Presence) Presence Pulse

Step 3 TX CCh Issue Skip ROM Command

TX 99h

Issue Copy Scratchpad with Password

Command

TX C0h TA1, Target Address = C0h

TX 7Fh TA2, Target Address = 7FC0h

TX 0Fh E/S-byte

TX <8 Bytes>

Transmit 8 Dummy Bytes as Password,

Because Passwords are Not Yet Enabled

(—) (Activate Strong Pullup for t

PROG

) Supply Power for Programming

RX AAh

Read to Check for Programming Success;

AAh Means Success

TX (Reset) Reset Pulse

RX (Presence) Presence Pulse

Step 4 TX CCh Issue Skip ROM Command

TX C3h Issue Verify Password Command

TX C0h

TA1, Target Address = C0h (Read Password

Address)

TX 7Fh TA2, target address = 7FC0h

TX <Read Password> Transmit Read Password

(—) (Activate Strong Pullup for t

PROG

) Supply Power for Password Comparison

RX AAh Check for Password Match; AAh = Match

TX (Reset) Reset Pulse

RX (Presence) Presence Pulse

TX CCh Issue Skip ROM Command

TX C3h Issue Verify Password Command

TX C8h

TA1, Target Address = C8h (Full-Access

DS1977

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MASTER MODE

DATA (LSB FIRST)

COMMENTS

Password Address)

TX 7Fh TA2, Target Address = 7FC8h

TX <Full-Access Password> Transmit Full-Access Password

(—) (Activate Strong Pullup for t

PROG

) Supply Power for Password Comparison

RX AAh Check for Password Match; AAh = Match

TX (Reset) Reset Pulse

RX (Presence) Presence Pulse

Step 5 TX CCh Issue Skip ROM Command

TX 0Fh Issue Write Scratchpad Command

TX D0h

TA1, Target Address = D0h (Password

Control Register Address)

TX 7Fh TA2, Target Address = 7FD0h

TX AAh Write Password Enabling Pattern

TX (Reset) Reset Pulse

RX (Presence) Presence Pulse

TX CCh Issue Skip ROM Command

TX AAh Issue Read Scratchpad Command

RX D0h Read TA1, Target Address = D0h

RX 7Fh Read TA2, Target Address = 7FD0h

RX 10h Read E/S-Byte

RX AAh Verify Password Enabling Pattern

TX (Reset) Reset Pulse

RX (Presence) Presence Pulse

TX CCh Issue Skip ROM Command

TX 99h

Issue Copy Scratchpad with Password

Command

TX D0h TA1, Target Address = D0h

TX 7Fh TA2, Target Address = 7FD0h

TX 10h E/S-Byte

TX <8 Bytes>

Transmit 8 Dummy Bytes as Password,

Because Passwords are Not Yet Enabled

(—) (Activate Strong Pullup for t

PROG

) Supply Power for Programming

RX AAh

Read to Check for Programming Success;

AAh Means Success

TX (Reset) Reset Pulse

RX (Presence) Presence Pulse

Instead of always using Skip ROM, one could use Read ROM first to learn the device's ROM identification (see

Example 1). For the next access one would use the Match ROM command and send the correct ROM identification

to address the device. Subsequent accesses could use the Resume command. This procedure ensures that

devices cannot be swapped during a communication session.

EXAMPLE 3

Task: write 10 data bytes starting at address 00A0h in page 2; read memory pages 2 and 3. The device has

passwords installed and activated. This task is broken into the following steps:

1. Write data to scratchpad

2. Read Scratchpad

3. Copy scratchpad

4. Read the entire memory page 3

5. Continue reading through the end of page 4

P1-P3 P4-P6 P7-P9 P10-P12 P13-P15 P16-P18 P19-P21 P22-P24 P25-P27 P28-P29

DS1977-F5#

Mfr. #:

Buy DS1977-F5#

Manufacturer:

Maxim Integrated

Description:

iButtons & Accessories Password-Protected 32KB EEPROM iButton

Lifecycle:

New from this manufacturer.

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DS1977-F5#