DS1923-F5#W Maxim Integrated Products, DS1923-F5#W Datasheet - Page 11

• Manufacturer Part Number: DS1923-F5#W
• Description: Board Mount Temperature Sensors Hygrochron Temp/Hum Logger w/8KB DataLog
• Manufacturer: Maxim Integrated Products

Specifications of DS1923-F5#W

• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

The DS1923 is an ideal device to monitor for extended
periods of time the temperature and humidity of any
object it is attached to or shipped with, such as fresh
produce, medical drugs and supplies, and for use in
refrigerators and freezers, as well as for logging climat-
ic data during the transport of sensitive objects and
critical processes such as curing. A 1.27mm diameter
hole in the lid of the device allows for air to reach the
humidity sensor. The rest of the electronics inside the
DS1923 is sealed so that it is not exposed to ambient
humidity. Note that the initial sealing level of the
DS1923 achieves the equivalent of IP56. Aging and use
conditions can degrade the integrity of the seal over
time, so for applications with significant exposure to liq-
uids, sprays, or other similar environments, it is recom-
mended to place the Hygrochron™ under a shield to
protect it (refer to Application Note 4126: Understanding
the IP (Ingress Protection) Ratings of iButton Data
Loggers and Capsule ). The hydrophobic filter may not
protect the DS1923 from destruction in the event of full
submersion in liquid. Software for setup and data
retrieval through the 1-Wire interface is available for free
download from the iButton website (www.ibutton.com).
This software also includes drivers for the serial and USB
port of a PC and routines to access the general-purpose
memory for storing application-specific or equipment-
specific data files.
The block diagram in Figure 1 shows the relationships
between the major control and memory sections of the
DS1923. The device has six main data components:
64-bit lasered ROM; 256-bit scratchpad; 512-byte gen-
eral-purpose SRAM; two 256-bit register pages of time-
keeping, control, status, and counter registers and
passwords; 64 bytes of calibration memory; and 8192
bytes of data-logging memory. Except for the ROM and
the scratchpad, all other memory is arranged in a sin-
gle linear address space. The data-logging memory,
counter registers, and several other registers are read
only for the user. Both register pages are write protect-
ed while the device is programmed for a mission. The
password registers, one for a read password and
another one for a read/write password, can only be writ-
ten, never read.
Hygrochron is a trademark of Maxim Integrated Products, Inc.
Hygrochron Temperature/Humidity Logger
______________________________________________________________________________________
Detailed Description
iButton with 8KB Data-Log Memory
Overview
Figure 2 shows the hierarchical structure of the 1-Wire
protocol. The bus master must first provide one of the
eight ROM function commands: Read ROM, Match
ROM, Search ROM, Conditional Search ROM, Skip
ROM, Overdrive-Skip ROM, Overdrive-Match ROM, or
Resume. Upon completion of an Overdrive-ROM com-
mand executed at standard speed, the device enters
overdrive mode, where all subsequent communication
occurs at a higher speed. The protocol required for
these ROM function commands is described in Figure
11. After a ROM function command is successfully exe-
cuted, the memory and control functions become
accessible and the master can provide any one of the
eight available commands. The protocol for these mem-
ory and control function commands is described in
Figure 9. All data is read and written least significant
bit first.
The block diagram (Figure 1) shows the parasite-pow-
ered circuitry. This circuitry “steals” power whenever
the IO input is high. IO 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 can still be read.
Each DS1923 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 cyclic redundancy check (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 regis-
ter and XOR gates as shown in Figure 4. The polynomi-
al is X
1-Wire CRC is available in Application Note 27:
Understanding and Using Cyclic Redundancy Checks
with Maxim iButton Products .
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 8th bit of the family code
has been entered, the serial number is entered. After
the last bit of the serial number has been entered, the
shift register contains the CRC value. Shifting in the 8
bits of CRC returns the shift register to all 0s.
8
+ X
5
+ X
4
+ 1. Additional information about the
64-Bit Lasered ROM
Parasite Power
11