Reverse Compatibility of the D

文章摘要：Operating Modes Configuration Register Thermostat Trip Point Registers (TH/TL) Temperature-to-Digital Conversion Time Operating ModesTo increase compatibility with the DS1621, the DS1721 was designed to operate in two modes: 1621 mode and standard mode. The DS1721 powers-up in 1621 mode, and will re

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

1. Operating Modes
2. Configuration Register
3. Thermostat Trip Point Registers (TH/TL)
4. Temperature-to-Digital Conversion Time

Operating Modes

To increase compatibility with the DS1621, the DS1721 was designed to operate in two modes: 1621 mode and standard mode. The DS1721 powers-up in 1621 mode, and will remain in this mode as long as temperature conversions are always initiated using the DS1621's Start Convert T command (EEh). In 1621 mode, the operation of the DS1721 is very similar to the DS1621 and the user retains the option of reading the slope accumulator and counter registers for high-resolution temperature calculations as described in Application Note 105. The DS1721 can be switched into standard mode by initiating temperature conversions using the DS1721's Start Convert T command (51h). Once the device is in standard mode, it will remain in this mode until the power is cycled, and the EEh Start Convert T command will be ignored.

The remainder of this application note assumes that the DS1721 is being used in 1621 mode (i.e., EEh is used to initiate all temperature conversions). Refer to the DS1721 datasheet for standard mode operating instructions for the device.

Configuration Register

There are several differences between the configuration registers of the DS1621 and DS1721. A primary difference is that in the DS1621 certain bits in the configuration register are stored in EEPROM. Figures 1 and 2 show the DS1621 and DS1721 configuration registers, with EEPROM bits underlined in the DS1621 configuration register and differences between the two devices boldfaced in the DS1721 configuration register. The following paragraphs describe in detail these differences and any incompatibilities created by these differences.


Figure 1. DS1621 Configuration register.


Figure 2. DS1721 Configuration register.

Bit 4 serves different purposes in the DS1621 and DS1721, but it does not create an incompatibility between the two devices. In both devices bit 4 is read only and cannot be overwritten by the user. Therefore, during writes to the configuration register the value written to Bit 4 is ignored.

Bit 4 in the DS1621 configuration register (NVB) is used to signal EEPROM status to the user as follows: NVB=0—EEPROM is not busy, NVB=1—EEPROM is being written to. Bit 4 in the DS1721 (U) indicates whether the device is in 1621 mode (U=0) or in standard mode (U=1). If the DS1721 is used in 1621 mode, bit 4 of the DS1721 will power-up as a 0 and remain a 0. If the standard mode Start Convert T command (51h) issued, bit 4 will change to a 1.

Bit 3 and Bit 2 serve different purposes in the DS1621 and DS1721, but they do not create an incompatibility between the two devices. In the DS1621 these bits are read only and are used internally by the device. In the DS1721 in 1621 mode, the R1 and R0 bits are read only and will power-up as R1=1 and R0=1. In 1621 mode, writing to these bits has no affect on the bits or on the operation of the device. If the DS1721 is used in standard mode, bits R1 and R0 define the readout resolution of the device (i.e., 9, 10, 11 or 12 bits). Refer to the DS1721 data sheet for more information about the use of R1 and R0 in standard mode.

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