DS1923_1 Datasheet, PDF (20/53 Pages) Dallas Semiconductor – Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory

DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
Bit Description
Bit(s)
Definition
This bit specifies the format used to store humidity readings in the data
HLFS: Humidity Logging
Format Selection
b3
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 is used (higher resolution). With 16-bit format,
the most-significant byte is stored at the lower address.
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
RO: Rollover Control
b4 logging continues at the beginning, overwriting previously collected data.
If this bit is 0, the logging and conversions will stop once the data log
memory is full. However, the RTC will continue to run and the MIP bit
will remain set until the Stop Mission command is performed.
This bit specifies whether a mission begins immediately (includes
delayed start) or if a temperature alarm will be required to start the
mission. If this bit is 1, the device will perform a temperature conversion
SUTA: Start Mission upon
Temperature Alarm
at the selected sample rate and begin with data logging only if an
b5 alarming temperature (high alarm or low alarm) was found. The first
logged temperature will be when the alarm occurred. However, the
Mission Sample Counter will not increment. The Start Upon Tempera-
ture Alarm function is only available if temperature logging is enabled
(ETL = 1).
ALARM STATUS
The fastest way to determine whether a programmed temperature or humidity threshold was exceeded during a
mission is through reading the Alarm Status Register. In a networked environment that contains multiple DS1923
iButtons the devices that encountered an alarm can quickly be identified by means of the Conditional Search
command (see ROM Function Commands). The humidity and temperature alarm only occurs if enabled (see
Temperature Sensor Alarm and Humidity Alarm). The BOR alarm is always enabled.
Alarm Status Register Bitmap
ADDR b7
b6
b5
b4
b3
b2
b1
b0
0214h BOR
1
1
1
HHF HLF THF TLF
There is only read access to this register. Bits 4 to 6 have no function. They always read 1. All five alarm status bits
are cleared simultaneously when the Clear Memory function is invoked. See Memory and Control Functions for
details.
Register Details
Bit Description
TLF: Temperature Low
Alarm Flag
THF: Temperature High
Alarm Flag
HLF: Humidity Low Alarm
Flag
HHF: Humidity High Alarm
Flag
BOR: Battery On Reset
Alarm
Bit(s)
b0
b1
b2
b3
b7
Definition
If this bit reads 1, there was at least one temperature conversion during
a mission revealing a temperature equal to or lower than the value in the
Temperature Low Alarm Register. A forced conversion can affect the
TLF bit. This bit can also be set with the initial alarm in the SUTA = 1
mode.
If this bit reads 1, there was at least one temperature conversion during
a mission revealing a temperature equal to or higher than the value in
the Temperature High Alarm Register. A forced conversion can affect
the THF bit. This bit can also be set with the initial alarm in the SUTA =
1 mode.
If this bit reads 1, there was at least one humidity reading during a
mission revealing a value equal to or lower than the value in the Humi-
dity Low Alarm Register. A forced conversion can affect the HLF bit.
If this bit reads 1, there was at least one humidity reading during a
mission revealing a value equal to or higher than the value in the Humi-
dity High Alarm Register. A forced conversion can affect the HHF bit.
If this bit reads 1, the device has performed a power-on reset. This
indicates that the device has experienced a shock big enough to
interrupt the internal battery power supply. The device can still appear
functional, but it has lost its factory calibration. Any data found in the
data log memory should be disregarded.
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