Datasheet

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