DS1977-F5- MAXIM [Maxim Integrated Products], DS1977-F5- Datasheet - Page 27

• Manufacturer Part Number: DS1977-F5-
• Description: Password-Protected 32KB EEPROM iButton
• Manufacturer: MAXIM [Maxim Integrated Products]

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:
Step 5
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
MASTER MODE
(—)
(—)
TX
RX
RX
RX
RX
RX
RX
RX
RX
RX
RX
TX
TX
TX
TX
TX
TX
TX
TX
TX
TX
TX
TX
TX
TX
TX
TX
TX
TX
(Activate Strong Pullup for t
(Activate Strong Pullup for t
<Full-Access Password>
DATA (LSB FIRST)
(Presence)
(Presence)
(Presence)
(Presence)
<8 Bytes>
(Reset)
(Reset)
(Reset)
(Reset)
CCh
CCh
CCh
AAh
D0h
AAh
AAh
D0h
AAh
D0h
AAh
7Fh
0Fh
7Fh
7Fh
7Fh
10h
99h
10h
27 of 29
PROG
PROG
)
)
Password Address)
TA2, Target Address = 7FC8h
Transmit Full-Access Password
Supply Power for Password Comparison
Check for Password Match; AAh = Match
Reset Pulse
Presence Pulse
Issue Skip ROM Command
Issue Write Scratchpad Command
TA1, Target Address = D0h (Password
Control Register Address)
TA2, Target Address = 7FD0h
Write Password Enabling Pattern
Reset Pulse
Presence Pulse
Issue Skip ROM Command
Issue Read Scratchpad Command
Read TA1, Target Address = D0h
Read TA2, Target Address = 7FD0h
Read E/S-Byte
Verify Password Enabling Pattern
Reset Pulse
Presence Pulse
Issue Skip ROM Command
Issue Copy Scratchpad with Password
Command
TA1, Target Address = D0h
TA2, Target Address = 7FD0h
E/S-Byte
Transmit 8 Dummy Bytes as Password,
Because Passwords are Not Yet Enabled
Supply Power for Programming
Read to Check for Programming Success;
AAh Means Success
Reset Pulse
Presence Pulse
COMMENTS