Reverse Compatibility of the D

文章摘要：The conversion time difference between the DS1621 and DS1721 could cause an incompatibility if the application software incorporates a delay of less than 1.2 seconds before reading the temperature when the device is in one-shot mode. However, if the software monitors the DONE bit in the configuratio

Reverse Compatibility of the D,标签：计算机控制技术,工厂电气控制技术,http://www.88dzw.com

The conversion time difference between the DS1621 and DS1721 could cause an incompatibility if the application software incorporates a delay of less than 1.2 seconds before reading the temperature when the device is in one-shot mode. However, if the software monitors the DONE bit in the configuration register this problem can be avoided because the DONE bit will change to 1 when the conversion is completed. If the application uses the continuous conversion mode, there will be no issue with conversion time because the double-buffered temperature register always contains the result from the last completed conversion.

Summary

The DS1721 brings to the marketplace a relaxed-accuracy reduced-cost version of the popular DS1621 2-Wire Digital Thermometer and Thermostat. Although compatibility with the DS1621 was a major concern in the design of the DS1721, cost reductions implemented in the DS1721 prevent it from being a true drop-in replacement for all DS1621 applications.

The following features are identical for both the DS1621 and DS1721, and will not cause incompatibilities when transitioning to the DS1721:

1. Pinout
   
   
   
2. Surface-mount package (150mil SO8)
3. Power supply range (2.7V ≤ VDD ≤ 5.5V)
4. Temperature range (-55°C to 125°C)
5. 2-wire address byte (1001 A2A1A0)
6. 3-bit selectable addressability
7. Command protocol for:
   
   1. Read Temperature (AAh)
      
   2. Access TH (A1h)
      
   3. Access TL (A2h)
      
   4. Access Config (ACh)
      
   5. Start Convert T (EEh)
      
   6. Stop Convert T (22h)
8. Programmable conversion modes (one-shot and continuous)
9. Programmable thermostat limits
10. Programmable thermostat output polarity

The following differences could disallow DS1721 drop-in compatibility in a socket designed for the DS1621, depending upon the specific application:

1. DS1721 thermometer accuracy is ±1.0°C over the range -10°C to +85°C. DS1621 thermometer accuracy is ±0.5°C over the range 0°C to +70°C.
2. The DS1721 does not have EEPROM for the thermostat trip points TH and TL. Their power-up defaults are +80°C and +75°C, respectively, in the DS1721.
3. The DS1721 configuration register bits 1SHOT and POL are not EEPROM, and will always power up to 0 (continuous conversion mode) and 1 (TOUT=active high), respectively.
4. Conversion time for DS1721 (used in 1621 mode) is 1.2 seconds (max). Conversion time for the DS1621 is 1 second (max).

If you require further information about transitioning your application from the DS1621 to the DS1721, please contact Thermal.Support@dalsemi.com or (972) 371-4448. The current DS1721 datasheet can be downloaded from: http://www.maxim-ic.com/quick_view2.cfm/qv_pk/2765

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