DS1721 Maxim Integrated Products, DS1721 Datasheet
DS1721
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DS1721 Summary of contents
Page 1
... DS1721 over a simple 2-wire serial interface. No additional components are required; the device is truly a “temperature-to-digital” converter. The DS1721 has three address bits that allow a user to multidrop up to eight sensors along the 2-wire bus, greatly simplifying the bussing of distributed temperature sensing networks. ...
Page 2
... Thermostat comparator The factory-calibrated temperature sensor requires no external components. Upon power-up, the DS1721 idle mode. Upon issuance of a Start Convert T command [51h], the DS1721 begins temperature conversions with the default resolution of 12 bits (0.0625°C resolution). Following an 8-bit command protocol, temperature data can be read over the 2-wire interface. The host can periodically read the value in the temperature register, which contains the last completed conversion ...
Page 3
... TL. Thus, any hysteresis can be realized for fan control without external components. Digital data is written to/read from the DS1721 via a 2-wire interface, and all communication is MSb first. Multipoint sensing is possible with the DS1721 by uniquely setting the 3-bit address eight parts on the 2-wire bus. DS1721 FUNCTIONAL BLOCK DIAGRAM Figure 1 ...
Page 4
... Regardless of the mode used, the digital temperature is retrieved from the temperature register using the Read Temperature (AAh) command, as described in detail in the “Command Set” section. The DS1721 power-up default has the sensor set to automatically perform 12-bit conversions continuously once the Start Convert T (51h) command is issued. Details on how to change the settings after power-up are contained in the “ ...
Page 5
... POL bit, and the power-up default state is "1" (active high Undefined. This bit is used internally by the DS1721. It will be a "0" at power-up and will change to a "1" once the Start Convert T [51h] command is issued. This is a “Don’t Care” write; i.e. The DS1721 will ignore writes to this location. bit of the 2-wire control byte (See “ ...
Page 6
... X = Undefined. These bits are used internally by the DS1721. DONE = Temperature Conversion Status Bit. "1" = conversion complete and "0" = conversion in progress. The DONE bit is read-only, and the power-up state is "1". In the continuous conversion mode, DONE = "0". ...
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... If the user does not wish to take advantage of the thermostat capabilities of the DS1721, the 24 bits can be used for general storage of system data that need not be maintained following a power loss. However, the T pin should be left floating if general data is stored in T OUT 2-WIRE SERIAL DATA BUS The DS1721 supports a bi-directional 2-wire bus and data transmission protocol ...
Page 8
... Slave transmitter mode: The first byte is received and handled as in the slave receiver mode. However, in this mode, the direction bit will indicate that the transfer direction is reversed. Serial data is transmitted on SDA by the DS1721 while the serial clock is input on SCL. START and STOP conditions are recognized as the beginning and end of a serial transfer. ...
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... SERIAL COMMUNICATION WITH DS1721 Figure DS1721 ...
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... START condition from the master device. The control byte consists of a 4-bit control code; for the DS1721, this is set as 1001 binary for read and write operations. The next 3 bits of the control byte are the device select bits (A2, A1, A0). They are used by the master device to select which of eight devices are to be accessed ...
Page 11
... This command stops temperature conversion. No further data is required. This command may be used to halt a DS1721 in continuous conversion mode. After issuing this command, the current temperature measurement will be completed, stored and the DS1721 will remain idle until a Start Convert T is issued to resume conversions. ...
Page 12
... Bus Master sends read temperature protocol ACK DS1721 generates acknowledge bit START Bus Master initiates a repeated START condition <address, 1> Bus Master sends DS1721 address; R/ ACK DS1721 generates acknowledge bit <1 data byte> DS1721 transmits MSB of temperature ACK Bus Master generates acknowledge bit < ...
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... SAMPLE COMMAND SEQUENCE Table 6 Example: Bus master programs the DS1721 for 11-bit conversions in the continuous mode with an active low state for the thermostat output. It then programs TH=50°C and TL=45°C and starts temperature conversions. BUS MASTER DS1721 MODE MODE ...
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... CONDITION MIN TYP 0 -0 sink 0 current 6 mA sink 0 current 1 mA source 2.4 current 4 mA sink current 0.4V V I/O -10 0 Active Temp. Conversions Communication only DS1721 V 5.5V) DD MAX UNITS NOTES 5 5.5V) DD MAX UNITS NOTES +0 ...
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... DD TYP MAX UNITS 0 400 KHz 0 100 µs µs µs µs µs 0 0.9 µ 300 ns C 1000 B 300 ns C 1000 B µs 400 DS1721 V 5.5V) DD NOTES 5 NOTES ...
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... SCL signal. If such a device does stretch the LOW period of the SCL signal, it must output the next data bit to the SDA line total capacitance of one bus line in pF. b TIMING DIAGRAMS Figure 7 TYPICAL DS1721 THERMOMETER PERFORMANCE CURVE Figure 8 MAX+t 1000+250 = 1250 ns before the SCL line is released. SU:DAT TBD DS1721 is switched off ...