DS1921L-F5X Datasheet, PDF (9/40 Pages) Dallas Semiconductor – Thermochron iButton

DS1921L
Control Register Bitmap
ADDR b7
b6
b5
b4
b3
b2
b1
b0
020Eh _EOSC EMCLR
0
EM
RO
TLS THS TAS
The functional assignments of the individual bits are explained in the table below. Bit 5 has no function.
It always reads 0 and cannot be written to 1.
Control Register Details
BIT DESCRIPTION
EOSC: Enable Oscillator
EMCLR: Memory Clear
Enable
EM: Enable Mission
RO: Rollover
Enable/Disable
TLS: Temperature Low
Alarm Search
THS: Temperature High
Alarm Search
TAS: Timer Alarm Search
BIT(S)
b7
b6
b4
b3
b2
b1
b0
DEFINITION
This bit controls the crystal oscillator of the RTC. When set to logic 0,
the oscillator will start operation. When written to logic 1, the oscillator
will stop and the device is in a low-power data retention mode. This bit
must be 0 for normal operation.
This bit needs to be set to logic 1 to enable the Clear Memory function,
which is invoked as a memory function command. The Time-Stamp,
Histogram Memory as well as the Mission Time Stamp, Mission
Samples Counter, Mission Start Delay and Sample Rate will be cleared
only if the Clear Memory command is issued with the next access to
the device. The EMCLR bit will return to 0 as the next memory function
command is executed.
This bit controls whether the DS1921L will begin a mission as soon as
the sample rate is written. To enable the device for a mission, this bit
must be 0.
This bit controls whether the temperature logging memory is overwritten
with new data or whether data logging is stopped once the memory is
filled with data during a mission. Setting this bit to a 1 enables the
rollover and data logging continues at the beginning overwriting
previously collected data. Clearing this bit to 0 disables the rollover and
no further temperature values will be stored in the temperature logging
memory once it is filled with data. This will not stop the mission. The
device will continue measuring temperatures and updating the
histogram.
If this bit is 1, the device will respond to a Conditional Search command
if during a mission the temperature has reached or is lower than the Low
Temperature Threshold stored at address 020Bh.
If this bit is 1, the device will respond to a Conditional Search command
if during a mission the temperature has reached or is higher than the
High Temperature Threshold stored at address 020Ch.
If this bit is 1, the device will respond to a Conditional Search command
if during a mission a timer alarm has occurred. Since a timer alarm
cannot be disabled, the TAF flag usually reads 1 during a mission.
Therefore it may be advisable to set the TAS bit to a 0, in most cases.
Mission Start Delay
The content of the Mission Start Delay register determines how many minutes will have to expire after
the beginning of a mission until the first temperature measurement of the mission occurs. The delay value
is stored as unsigned 16-bit integer number at addresses 212h (low byte) and 213h (high byte). The
maximum delay is 65535 minutes, equivalent to 45 days, 12 hours, and 15 minutes.
For a typical mission, the Mission Start Delay is 0. If a mission is too long for a single DS1921L to store
all temperature readings at the selected sample rate, one can use several devices and set the Mission Start
Delay for the second device to start recording as soon as the memory of the first device is full. The RO bit
in the control register (address 020Eh) must be set to 0 to prevent overwriting of the recorded temperature
log after the datalog memory is full.
9 of 40