Hygrochron Temperature/Humidity Logger

iButton with 8KB Data-Log Memory

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21

Bit 0: Enable Oscillator (EOSC). This bit controls the

crystal oscillator of the RTC. When set to logic 1, the

oscillator starts. 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

Forced Conversion or Start Mission command automati-

cally starts the RTC by changing the EOSC bit to

logic 1.

Mission Control

The DS1923 is set up for its operation by writing appro-

priate 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)

applies, and whether old data can be overwritten by

new data once the data-log memory is full. An addition-

al control bit can be set to tell the DS1923 to wait with

logging data until a temperature alarm is encountered.

Bit 5: Start Mission Upon Temperature Alarm

(SUTA). This bit specifies whether a mission begins

immediately (includes delayed start) or if a temperature

alarm is required to start the mission. If this bit is 1, the

device performs an 8-bit temperature conversion at the

selected sample rate and begins with data logging only

if an alarming temperature (high alarm or low alarm)

was found. The first logged temperature is when the

alarm occurred. However, the Mission Samples

Counter does not increment. The start upon tempera-

ture alarm function is only available if temperature log-

ging is enabled (ETL = 1).

Bit 4: Rollover Control (RO). This bit controls whether,

during a mission, the data-log memory is overwritten

with new data or whether data logging is stopped once

the data-log memory is full. Setting this bit to 1 enables

the rollover and data logging continues at the begin-

ning, overwriting previously collected data. If this bit is

0, the logging and conversions stop once the data-log

memory is full. However, the RTC continues to run and

the MIP bit remains set until the Stop Mission command

is performed.

Bit 3: Humidity Logging Format Selection (HLFS).

This bit specifies the format used to store humidity

readings in the data-log memory. If this bit is 0, the

data is stored in 8-bit format. If this bit is 1, the 16-bit

format is used (higher resolution). With 16-bit format,

the most significant byte is stored at the lower address.

Bit 2: Temperature Logging Format Selection

(TLFS). This bit specifies the format used to store tem-

perature readings in the data-log memory. If this bit is

0, the data is stored in 8-bit format. If this bit is 1, the

16-bit format is used (higher resolution). With 16-bit for-

mat, the most significant byte is stored at the lower

address.

Bit 1: Enable Humidity Logging (EHL). 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 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 tempera-

ture, typically both humidity and temperature logging

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

Bit 0: Enable Temperature Logging (ETL). 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.

Mission Control Register Bitmap

ADDRESS

BIT 7

BIT 6

BIT 5

BIT 4

BIT 3

BIT 2

BIT 1

BIT 0

0213h

1

1

SUTA

RO

HLFS

TLFS

EHL

ETL

Note: 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.