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DS1921Z Datasheet(PDF) 9 Page - Dallas Semiconductor |
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DS1921Z Datasheet(HTML) 9 Page - Dallas Semiconductor |
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9 / 45 page  DS1921H/Z 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. 9 of 45 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 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. |
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