DS1925 datasheet(16/46 Pages) MAXIM

16 / 46 page

Mission Progress Indicator

Depending on settings in the Mission Control register

(address 0213h), the DS1925 logs temperature in 8-bit

or 16-bit format. The Mission Samples Counter register

together with the starting address and the logging format

(8 or 16 bits) provides the information to identify valid

blocks of data that have been gathered during the current

(MIP = 1) or latest mission (MIP = 0). See the Data-Log

Memory Usage section for an illustration. See Table 20

for the register bitmap. There is only read access to this

The number read from the Mission Samples Counter

indicates how often the DS1925 woke up during a mis-

sion to measure temperature. The number format is 24-bit

unsigned integer. The Mission Samples Counter is reset

through the XPC Clear Memory command

Other Indicators

The Device Samples Counter is similar to the Mission

Samples Counter. During a mission this counter incre-

ments whenever the DS1925 wakes up to measure and

log data and when the device is testing for a temperature

alarm in SUTA mode. This way the Device Samples

Counter functions like a gas gauge for the battery that

powers the iButton device. There is only read access to

this register.

The Device Samples Counter is reset to zero when the

iButton device is assembled. The counter increments a

couple of times during final test. The number format is

24-bit unsigned integer. The maximum number that can

be represented in this format is 16777215.

The Device Configuration byte is used to allow the master

to distinguish between the different versions of the iButton

logger devices. Table 22 shows the codes assigned to the

various devices. There is only read access to this register.

Security by Password

The DS1925 is designed to use two passwords that con-

trol read access and full access. Reading from or writing

to the scratchpad as well as the XPC Forced Conversion

command do not require a password. The password

needs to be transmitted right after the command code

of the memory or control function. 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 pass-

word checking is enabled. See Table 23 for the register

bitmap. During a mission, there is only read access to

this register.

Table 20. Mission Samples Counter Register Bitmap

Table 21. Device Samples Counter Register Bitmap

Table 22. Device Configuration Byte (0226h)

DS1925

iButton High-Capacity Temperature Logger

with 122KB Data-Log Memory

www.maximintegrated.com

Maxim Integrated │ 16

ADDR

0220h

Low Byte

0221h

Center Byte

0222h

High Byte

ADDR

0223h

Low Byte

0224h

Center Byte

0225h

High Byte

ADDR

DEVICE

0226h

DS2422

0226h

DS1923

0226h

DS1922L

0226h

DS1922T

0226h

DS1922E

0226h

DS1925

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