DS1923 Maxim, DS1923 Datasheet - Page 12

• Manufacturer Part Number: DS1923
• Description: The DS1923 temperature/humidity logger iButton® is a rugged, self-sufficient system that measures temperature and/or humidity and records the result in a protected memory section
• Manufacturer: Maxim

Hygrochron Temperature/Humidity Logger
iButton with 8KB Data-Log Memory
Figure 1. Block Diagram
read only for the user. Both register pages are write
protected while the device is programmed for a mis-
sion. The password registers, one for a read password
and another one for a read/write password, can only
be written, never read.
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
12
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3V LITHIUM
THERMAL
SENSOR AND
OSCILLATOR
HUMIDITY
SENSE
1-Wire PORT
32.768kHz
ADC2
IO
ADC1
DS1923
CONTROL REGISTERS,
AND COUNTERS
CONTROL
TIMEKEEPING,
LOGIC
INTERNAL
FUNCTION
CONTROL
ROM
CALIBRATION MEMORY
DATA-LOG MEMORY
GENERAL-PURPOSE
REGISTER PAGES
accessible and the master can provide any one of the
eight available commands. The protocol for these
memory and control function commands is described
in Figure 9. All data is read and written least signifi-
cant 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 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 DS1923 is solely operated by battery energy.
(512 BYTES)
(64 BYTES)
(64 BYTES)
SRAM
LASERED
8KB
64-BIT
ROM
FUNCTION
CONTROL
MEMORY
PARASITE-POWERED
CIRCUITRY
SCRATCHPAD
256-BIT
Parasite Power