DS1921H データシートの表示（PDF） - Maxim Integrated

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DS1921H

High-Resolution Thermochron iButton Range H: +15°C to +46°C; Z: -5°C to +26°C

Maxim Integrated 

DS1921H/Z

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

1-Wire

IO

Port

ROM

Function

Control

64-Bit

Lasered

ROM

Parasite

Powered

Circuitry

Memory

Function

Control

256-Bit

Scratchpad

General-Purpose

SRAM

32.768kHz

Oscillator

Internal

Timekeeping &

Control Reg. &

Counters

Register Page

Alarm Time Stamp

and Duration

Logging Memory

Temperature

Sensor

Control

Logic

Histogram Memory

3V Lithium

Datalog

Memory

PARASITE POWER

The block diagram (Figure 1) shows the parasite-powered circuitry. This circuitry “steals” power when-

ever the IO input is high. IO will provide sufficient power as long as the specified timing and voltage re-

quirements are met. The advantages of parasite power are two-fold: 1) by parasiting off this input, lithium

is conserved, and 2) if the lithium is exhausted for any reason, the ROM may still be read normally.

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 X8 + X5 + X4 + 1. Additional information about the Dallas 1-Wire Cyclic Redundancy Check is avail-

able in Application Note 27 and in the Book of DS19xx iButton Standards.

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