DS1923 Datasheet, PDF(19/52 Page) Dallas Semiconductor – Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory

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DS1923 Datasheet, PDF (19/52 Pages) Dallas Semiconductor – Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory

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DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory

REAL-TIME CLOCK CONTROL

To minimize the power consumption of a DS1923, the real-time clock oscillator should be turned off when device is

not in use. The oscillator on/off bit is located in the RTC control register. This register also includes the EHSS bit,

which determines whether the sample rate is specified in seconds or minutes.

RTC Control Register Bitmap

ADDR b7

0212h

EHSS EOSC

During a mission, there is only read access to this register. Bits 2 to 7 have no function. They always read 0 and

cannot be written to 1.

Bit Description

EOSC: Enable Oscillator

EHSS: Enable High Speed

Sample

Bit(s)

Definition

This bit controls the crystal oscillator of the real-time clock. When set to

logic 1, the oscillator starts operation. When written to logic 0, the

oscillator stops and the device is in a low-power data retention mode.

This bit must be 1 for normal operation. A temperature or humidity

conversion must not be attempted while the RTC oscillator is

stopped. This causes the device to enter into an unrecoverable state.

This bit controls the speed of the Sample Rate counter. When set to

logic 0, the sample rate is specified in minutes. When set to logic 1, the

sample rate is specified in seconds.

MISSION CONTROL

The DS1923 is set up for its operation by writing appropriate data to its special function registers, which are located

in the two register pages. The settings in the Mission Control Register determine whether temperature and/or

humidity is logged, which format (8 or 16 bits) is to be used and whether old data can be overwritten by new data,

once the data log memory is full. An additional control bit can be set to tell the DS1923 to wait with logging data

until a temperature alarm is encountered.

Mission Control Register Bitmap

ADDR b7

0213h

SUTA RO HLFS TLFS EHL ETL

During a mission, there is only read access to this register. Bits 6 and 7 have no function. They always read 1 and

cannot be written to 0.

Bit Description

ETL: Enable Temperature

Logging

EHL: Enable Humidity

Logging

TLFS: Temperature

Logging Format Selection

Bit(s)

Definition

To set up the device for a temperature-logging mission, this bit must be

set to logic 1. To successfully start a mission, ETL or EHL must be 1. If

temperature logging is enabled, the recorded temperature values are

always stored starting at address 1000h.

To set up the DS1923 for a humidity-logging mission, this bit must be

set to logic 1. If temperature and humidity logging are enabled, the

recorded humidity values will begin at address 2000h (TLFS = HLFS) or

1A00h (TLFS = 0; HLFS = 1) or 2400h (TLFS = 1; HLFS = 0). If only

humidity logging is enabled, the recorded values are stored starting at

address 1000h. Since humidity data has little scientific value without

knowing the temperature, typically both, humidity and temperature

logging are enabled, i. e., ETL and EHL are set to 1.

This bit specifies the format used to store temperature readings in the

data log memory. If this bit is 0, the data will be stored in 8-bit format. If

this bit is 1, the 16-bit format will be used (higher resolution). With 16-bit

format, the most-significant byte is stored at the lower address.

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