DS1921H_11 MAXIM [Maxim Integrated Products], DS1921H_11 Datasheet - Page 3

• Manufacturer Part Number: DS1921H_11
• Description: High-Resolution Thermochron iButton
• Manufacturer: MAXIM [Maxim Integrated Products]

the seven available commands. The protocol for these memory function commands is described in Figure
10. All data is read and written least significant bit first.
DS1921H/Z BLOCK DIAGRAM Figure 1
PARASITE POWER
The block diagram (Figure 1) shows the parasite-powered circuitry. This circuitry “steals” power
whenever the IO input is high. IO will provide 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 may still be read normally. The remaining circuitry of the DS1921 is
solely operated by battery energy.
64-BIT LASERED ROM
Each DS1921 contains a unique ROM code that is 64 bits long. The first eight bits are a 1-Wire family
code. The next 36 bits are a unique serial number. The next 12 bits, called temperature range code, allow
distinguishing the DS1921H and DS1921Z from each other and from other DS1921 versions. The last
eight bits are a 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 register and XOR gates as shown in Figure 4. The polynomial
is X
available in Application Note 27.
8
+ X
1-Wire
Temperature
Port
5
Sensor
+ X
32.768kHz
Oscillator
4
+ 1. Additional information about the Maxim 1-Wire Cyclic Redundancy Check is
IO
3V Lithium
Control
Logic
Timekeeping &
Control Reg. &
Function
Control
ROM
Counters
Internal
3 of 45
Histogram Memory
Alarm Time Stamp
General-Purpose
Logging Memory
Register Page
and Duration
Lasered
64-Bit
Memory
ROM
Datalog
SRAM
Function
Memory
Control
Powered
Parasite
Circuitry
Scratchpad
256-Bit