DS1922T Maxim, DS1922T Datasheet - Page 25

• Manufacturer Part Number: DS1922T
• Description: The DS1922L/T temperature logger iButtons® are rugged, self-sufficient systems that measure temperature and record the result in a protected memory section
• Manufacturer: Maxim

The Device Samples Counter register is similar to the
Mission Samples Counter register. During a mission this
counter increments whenever the DS1922L/DS1922T
wake up to measure and log data and when these
devices are testing for a temperature alarm in SUTA
mode. Between missions, the counter increments when-
ever the Forced Conversion command is executed. This
way the Device Samples Counter register functions like
a gas gauge for the battery that powers the iButton.
The Device Samples Counter register is reset to zero
when the iButton is assembled. The number format is
24-bit unsigned integer. The maximum number that can
be represented in this format is 16,777,215. Due to the
calibration and tests at the factory, new devices can
have a count value of up to 35,000. The typical value is
well below 10,000.
The code in the Device Configuration register allows
the master to distinguish between the DS2422 chip and
different versions of the DS1922 iButtons. The Device
Configuration Register Bitmap shows the codes
assigned to the various devices.
Note: There is only read access to this register.
Note: There is only read access to this register.
Note: During a mission, there is only read access to this register.
ADDRESS
ADDRESS
ADDRESS
0226h
0223h
0224h
0225h
0227h
BIT 7
0
0
0
0
1
BIT 7
BIT 7
______________________________________________________________________________________
Temperature Logger iButton with 8KB
BIT 6
0
0
1
1
0
BIT 6
BIT 6
Other Indicators
BIT 5
0
1
0
1
0
BIT 5
BIT 5
BIT 4
0
0
0
0
0
BIT 4
BIT 4
Center Byte
High Byte
Low Byte
The DS1922L/DS1922T are designed to use two pass-
words that control read access and full access.
Reading from or writing to the scratchpad as well as the
Forced Conversion command does not require a pass-
word. The password must be transmitted immediately
after the command code of the memory or control func-
tion. If password checking is enabled, the password
transmitted is compared to the passwords stored in the
device. The data pattern stored in the Password Control
register determines whether password checking is
enabled.
To enable password checking, the EPW bits need to
form a binary pattern of 10101010 (AAh). The default
pattern of EPW is different from AAh. If the EPW pattern
is different from AAh, any pattern is accepted as long
as it has a length of exactly 64 bits. Once enabled,
changing the passwords and disabling password
checking requires the knowledge of the current full-
access password.
BIT 3
Device Samples Counter Register Bitmap
EPW
0
0
0
0
0
Device Configuration Register Bitmap
BIT 3
BIT 3
Password Control Register Bitmap
BIT 2
Data-Log Memory
0
0
0
0
0
BIT 2
BIT 2
BIT 1
0
0
0
0
0
Security by Password
BIT 1
BIT 1
BIT 0
0
0
0
0
0
DS1922L
DS1922T
DS1922E
DS2422
DS1923
BIT 0
BIT 0
PART
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