DS1922T-F5 MAXIM [Maxim Integrated Products], DS1922T-F5 Datasheet - Page 13

• Manufacturer Part Number: DS1922T-F5
• Description: Temperature Logger iButton With 8kB Datalog Memory
• Manufacturer: MAXIM [Maxim Integrated Products]

Figure 1. DS1922L/T Block Diagram
PARASITE POWER
The block diagram (Figure 1) shows the parasite-powered circuitry. This circuitry “steals” power whenever the I/O
input is high. I/O will provide sufficient power as long as the specified timing and voltage requirements are met. The
advantage of parasite power is that if the battery is exhausted for any reason, the ROM may still be read.
64-BIT LASERED ROM
Each DS1922L/T 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 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
Check (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
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.
3V Lithium
1-Wire
Port
th
8
32.768kHz
Oscillator
+ X
bit of the family code has been entered, then the serial number followed by the
Thermal
Sense
I/O
5
+ X
4
+ 1. Additional information about the Dallas 1-Wire Cyclic Redundancy
ADC
Timekeeping &
Control Reg. &
Function
Control
ROM
Counters
13 of 50
Control
Internal
Logic
Calibration Memory
General-Purpose
Register Pages
(512 Bytes)
Lasered
(64 Bytes)
(64 Bytes)
8k Bytes
64-Bit
Memory
ROM
Datalog
SRAM
Function
Memory
Control
Powered
Parasite
Circuitry
Scratchpad
256-Bit
DS1922L/DS1922T