Datasheet

DS1921H/Z
9 of 45
SAMPLE RATE
The content of the Sample Rate Register (address 020Dh) determines how many minutes the temperature
conversions are apart from each other during a mission. The sample rate may be any value from 1 to 255,
coded as an unsigned 8-bit binary number. If the memory has been cleared (Status Register bit MEMCLR
= 1) and a mission is enabled (Status Register bit EM = 0), writing a non-zero value to the Sample Rate
Register will start a mission. For a full description of the correct sequence of steps to start a temperature-
logging mission see sections Missioning or Missioning Example.
Sample Rate Register Map
ADDR
b7
b6
b5
b4
b3
b2
b1
b0
020Dh
Sample Rate
CONTROL REGISTER
The DS1921H/Z is set up for its operation by writing appropriate data to its special function registers that
are located in the register page. Several functions that are controlled by a single bit only are combined
into a single byte called Control Register (address 20Eh). This register can be read and written. If the
device is programmed for a mission, writing to the Control Register will end the mission and change the
register contents.
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
BIT(S)
DEFINITION
EOSC: Enable Oscillator
b7
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. The RTC must have advanced at
least 1 second before a mission start will be accepted.
EMCLR: Memory Clear
Enable
b6
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.
EM: Enable Mission
b4
This bit controls whether the DS1921H/Z will begin a mission as soon as
the sample rate is written. To enable the device for a mission, this bit
must be 0.
RO: Rollover
Enable/Disable
b3
This bit controls whether the datalog 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 datalog memory once it is filled
with data. This will not stop the mission. The device will continue
measuring temperatures and updating the histogram and alarm time
stamps and durations.