DS1921 datasheet(9/44 Pages) DALLAS

9 / 44 page

DS1921H/Z

9 of 44

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

logging mission see sections Missioning or Missioning Example.

Sample Rate Register Map

ADDR

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

Control Register Bitmap

ADDR

020Eh

EOSC

EMCLR

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

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

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

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

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 and alarm time stamps and durations.

DS1921 датащи(PDF) 9 Page - Dallas Semiconductor

DS1921 датащи(HTML) 9 Page - Dallas Semiconductor

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44

датащи скачать

ссылки URL