DS2422 Maxim, DS2422 Datasheet - Page 9

• Manufacturer Part Number: DS2422
• Description: The DS2422 temperature/data logger combines the core functions of a fully featured data logger in a single chip
• Manufacturer: Maxim

Figure 4. Hierarchical Structure for 1-Wire Protocol
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
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
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.
Master
Command
Level:
BUS
1-Wire ROM Function
Memory Function
DS2422-specific
Commands
Commands
1-Wire net
th
8
+ X
bit of the family code has been entered, then the serial number followed by the
DS2422
Available
Commands:
Read ROM
Match ROM
Search ROM
Conditional Search ROM
Skip ROM
Resume
Overdrive Skip
Overdrive Match
Write Scratchpad
Read Scratchpad
Copy Scratchpad w/PW
Read Memory w/PW &
Clear Memory w/PW
Forced Conversion
Start Mission w/PW
Stop Mission w/PW
5
w/CRC
+ X
4
+ 1. Additional information about the Dallas 1-Wire CRC is available in
9 of 49
Data Field
Affected:
64-bit ROM, RC-Flag
64-bit ROM, RC-Flag
64-bit ROM, RC-Flag
64-bit ROM, RC-Flag, Alarm Flags,
RC-Flag
RC-Flag
RC-Flag, OD-Flag
64-bit ROM, RC-Flag, OD-Flag
256-bit Scratchpad, Flags
256-bit Scratchpad
512 byte Data Memory, Registers,
Memory, Registers, Passwords
Mission Time Stamp, Mission Samples
Memory addresses 020C to 020Fh
Flags, Timestamp
Flags
Devices
Other
Counter, Start Delay, Sample
Rate Register, Alarm Flags,
Passwords
Search Conditions
Flags, Passwords