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DS2422S Datasheet(PDF) 9 Page - Dallas Semiconductor |
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DS2422S Datasheet(HTML) 9 Page - Dallas Semiconductor |
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9 / 48 page  DS2422 9 of 48 Figure 4. Hierarchical Structure for 1-Wire Protocol 1-Wire net Other Devices BUS Master DS2422 Available Commands: Command Level: Data Field Affected: 1-Wire ROM Function Commands DS2422-specific Memory Function Commands Read ROM Match ROM Search ROM Conditional Search ROM Skip ROM Resume Overdrive Skip Overdrive Match 64-bit ROM, RC-Flag 64-bit ROM, RC-Flag 64-bit ROM, RC-Flag 64-bit ROM, RC-Flag, Alarm Flags, Search Conditions RC-Flag RC-Flag RC-Flag, OD-Flag 64-bit ROM, RC-Flag, OD-Flag Write Scratchpad Read Scratchpad Copy Scratchpad w/PW Read Memory w/PW Read Memory w/PW & w/CRC Clear Memory w/PW Forced Conversion Start Mission w/PW Stop Mission w/PW 256-bit Scratchpad, Flags 256-bit Scratchpad 512 byte Data Memory, Registers, Flags, Passwords Memory, Registers, Passwords Memory, Registers, Passwords Mission Time Stamp, Mission Samples Counter, Start Delay, Sample Rate Register, Alarm Flags, Passwords Memory addresses 020C to 020Fh Flags, Timestamp Flags PARASITE POWER The block diagram (Figure 3) shows the parasite-powered 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 conserved; and 2) if the battery is exhausted for any reason, the ROM may still be read. 64-BIT LASERED ROM Each DS2422 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 CRC of the first 56 bits. See Figure 5 for details. The 1-Wire CRC is generated using a polynomial generator consisting of a shift register and XOR gates as shown in Figure 6. The polynomial is X 8 + X5 + X4 + 1. Additional information about the Dallas 1-Wire CRC is available in Application Note 27 and in the Book of DS19xx 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 8 th bit of the family code has been entered, then the serial number followed by the temperature range code is entered. After the range code has been entered, the shift register contains the CRC value. Shifting in the 8 bits of CRC returns the shift register to all 0s. |
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Similar Description - DS2422S |
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