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DS1922E-F5- Datasheet(PDF) 6 Page - Maxim Integrated Products |
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DS1922E-F5- Datasheet(HTML) 6 Page - Maxim Integrated Products |
6 / 44 page Detailed Description With its extended temperature range, the DS1922E is well suited to monitor processes that require tempera- tures well above the boiling point of water, such as pas- teurization of food items. Note that the initial sealing level of the DS1922E achieves the equivalent of IP56. Aging and use conditions can degrade the integrity of the seal over time, so for applications with significant exposure to liquids, sprays, or other similar environ- ments, it is recommended to place the DS1922E in the DS9107 iButton capsule. The DS9107 provides a water- tight enclosure that has been rated to IP68 (refer to Application Note 4126: Understanding the IP (Ingress Protection) Ratings of iButton Data Loggers and Capsules). Software for setup and data retrieval through the 1-Wire interface is available for free download from the iButton website (www.ibutton.com). This software also includes drivers for the serial and USB port of a PC and routines to access the general-purpose memory for storing application- or equipment-specific data files. Overview The block diagram in Figure 1 shows the relationships between the major control and memory sections of the DS1922E. The device has five main data components: 64-bit lasered ROM; 256-bit scratchpad; 576-byte gen- eral-purpose SRAM; two 256-bit register pages of time- keeping, control, status, and counter registers, and passwords; and 8192 bytes of data-logging memory. Except for the ROM and the scratchpad, all other mem- ory is arranged in a single linear address space. The data-logging memory, counter registers, and several other registers are read only for the user. Both register pages are write protected while the device is pro- grammed for a mission. The password registers, one for a read password and another one for a read/write pass- word, can only be written, never read. Figure 2 shows the hierarchical structure of the 1-Wire protocol. The bus master must first provide one of the eight ROM function commands: Read ROM, Match ROM, Search ROM, Conditional Search ROM, Skip ROM, Overdrive-Skip ROM, Overdrive-Match ROM, or Resume Command. Upon completion of an Overdrive ROM command byte executed at standard speed, the device enters Overdrive Mode, where all subsequent communication occurs at a higher speed. The protocol required for these ROM function commands is described in Figure 11. After a ROM function command is successfully executed, the memory and control func- tions become accessible and the master can provide any one of the eight available commands. The protocol for these memory and control function commands is described in Figure 9. All data is read and written least significant bit first. Parasite Power The block diagram (Figure 1) shows the parasite-pow- ered circuitry. This circuitry “steals” power whenever the I/O input is high. I/O provides sufficient power as long as the specified timing and voltage requirements are met. The advantages of parasite power are two-fold: 1) By parasiting off this input, battery power is not consumed for 1-Wire ROM function commands, and 2) if the battery is exhausted for any reason, the ROM can still be read normally. The remaining circuitry of the DS1922E is sole- ly operated by battery energy. 64-Bit Lasered ROM Each DS1922E contains a unique ROM code that is 64 bits long. The first 8 bits are a 1-Wire family code. The next 48 bits are a unique serial number. The last 8 bits are a cyclic redundancy check (CRC) of the first 56 bits (see Figure 3 for details). The 1-Wire CRC is generated using a polynomial generator consisting of a shift regis- ter and XOR gates as shown in Figure 4. The polynomi- al is X8 + X5 + X4 + 1. Additional information about the 1-Wire CRC is available in Application Note 27: Understanding and Using Cyclic Redundancy Checks with Maxim iButton Products and in Application Note 937: Book of iButton Standards. The shift register bits are initialized to 0. Then, starting with the least significant bit of the family code, one bit at a time is shifted in. After the 8th bit of the family code has been entered, the serial number is entered. After the last bit of the serial number has been entered, the shift register contains the CRC value. Shifting in the 8 bits of CRC returns the shift register to all 0s. High-Temperature Logger iButton with 8KB Data-Log Memory 6 _______________________________________________________________________________________ |
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