DS1977 Maxim, DS1977 Datasheet - Page 25

• Manufacturer Part Number: DS1977
• Description: The DS1977 is a 32KB EEPROM in a rugged iButton® enclosure
• Manufacturer: Maxim

VERIFY PASSWORD (SUCCESS)
VERIFY PASSWORD (FAIL ADDRESS OR PASSWORD)
READ VERSION (CANNOT FAIL)
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:
EXAMPLE 2
Task: Install and activate passwords; passwords are currently not activated
This task is broken into the following steps:
RST
RST
RST
1. Write new passwords to scratchpad
2. Read Scratchpad
3. Copy scratchpad
4. Verify new passwords
5. Activate password
MASTER MODE
PD
PD
PD
RX
RX
RX
RX
RX
TX
TX
TX
TX
TX
Select
Select
Select
VP
VP
RV
TA
TA
00h
<Version>, <Version>
DATA (LSB FIRST)
<8 Bytes ROM ID>
Password
Password
(Presence)
(Presence)
00h
00h, 00h
(Reset)
(Reset)
CCh
FFh
33h
Version
25 of 29
Strong Pullup
Strong Pullup
Version
Reset Pulse
Presence Pulse
Issue Read ROM Command
Read ROM ID
Issue Read Version Register Command
Write Two 00h Bytes
Read Chip Version Code Twice
Additional Reads Result in FFh Bytes
Reset Pulse
Presence pulse
FF loop
AA loop
FF loop
COMMENTS
DS1977