DS1921G-F5 查看數據表（PDF） - Maxim Integrated

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DS1921G-F5

Thermochron iButton

Maxim Integrated 

Thermochron iButton

histogram memory; and 2048 bytes of data-log mem-

ory. Except for the ROM and the scratchpad, all other

memory is arranged in a single linear address space.

All memory reserved for logging purposes, including

counter registers and several other registers, is read-

only for the user. The timekeeping and control regis-

ters are write protected while the device is

programmed for a mission.

The hierarchical structure of the 1-Wire protocol is

shown in Figure 2. The bus master must first provide

one of the seven ROM function commands: Read ROM,

Match ROM, Search ROM, Conditional Search ROM,

Skip ROM, Overdrive-Skip ROM, or Overdrive-Match

ROM. Upon completion of an Overdrive ROM com-

mand byte executed at standard speed, the device

enters overdrive mode, where all subsequent communi-

cation occurs at a higher speed. The protocol required

for these ROM function commands is described in

Figure 13. After a ROM function command is success-

fully executed, the memory functions become accessi-

ble and the master can provide any one of 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.

Parasite Power

Figure 1 shows the parasite-powered circuitry. This cir-

cuitry “steals” power whenever the IO input is high. IO

provides sufficient power as long as the specified tim-

ing 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 DS1921G is solely operated

by battery energy. As a consequence, if the battery is

exhausted, all memory data is lost including the data of

the last mission, and no new mission can be started.

Refer to Application Note 5057: OneWireViewer Tips

and Tricks for how to check the battery status.

BUS

MASTER

1-Wire NET

OTHER DEVICES

COMMAND LEVEL:

1-Wire ROM

FUNCTION COMMANDS

DS1921G-SPECIFIC

MEMORY/CONTROL

FUNCTION COMMANDS

AVAILABLE COMMANDS:

READ ROM

MATCH ROM

SEARCH ROM

SKIP ROM

OVERDRIVE-SKIP ROM

OVERDRIVE-MATCH ROM

CONDITIONAL SEARCH ROM

DS1921G

COMMAND CODES:

33h

55h

F0h

CCh

3Ch

69h

ECh

WRITE SCRATCHPAD

0Fh

READ SCRATCHPAD

AAh

COPY SCRATCHPAD

55h

READ MEMORY

F0h

READ MEMORY WTH CRC

A5h

CLEAR MEMORY

3Ch

CONVERT TEMPERATURE

44h

DATA FIELD AFFECTED:

64-BIT ROM

64-BIT ROM

64-BIT ROM

N/A

OD-FLAG

64-BIT ROM, OD-FLAG

64-BIT ROM, CONDITIONAL SEARCH

SETTINGS, DEVICE STATUS

256-BIT SCRATCHPAD, FLAGS

256-BIT SCRATCHPAD

4096-BIT SRAM, REGISTERS, FLAGS

ALL MEMORY

ALL MEMORY

MISSION TIMESTAMP, MISSION SAMPLES COUNTER,

START DELAY, SAMPLE RATE, ALARM TIMESTAMPS

AND DURATIONS, HISTOGRAM MEMORY

MEMORY ADDRESS 211h

Figure 2. Hierarchical Structure for 1-Wire Protocol

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