DS1922E-F5# Maxim Integrated Products, DS1922E-F5# Datasheet - Page 29

• Manufacturer Part Number: DS1922E-F5#
• Description: IBUTTON TEMP LOGGER 4KBit F5
• Manufacturer: Maxim Integrated Products
• Series: iButton®r

Specifications of DS1922E-F5#

• Rohs Information: IButton RoHS Compliance Plan
• Memory Size: 512B
• Memory Type: NVSRAM (Non-Volatile SRAM)
• Lead Free Status / RoHS Status: Lead free by exemption / RoHS compliant by exemption

The 1-Wire bus is a system that has a single bus mas-
ter and one or more slaves. In all instances the
DS1922E is a slave device. The bus master is typically
a microcontroller. The discussion of this bus system is
broken down into three topics: hardware configuration,
transaction sequence, and 1-Wire signaling (signal
types and timing). The 1-Wire protocol defines bus
transactions in terms of the bus state during specific
time slots that are initiated on the falling edge of sync
pulses from the bus master.
The 1-Wire bus has only a single line by definition; it is
important that each device on the bus be able to drive
it at the appropriate time. To facilitate this, each device
attached to the 1-Wire bus must have open-drain or
three-state outputs. The 1-Wire port of the DS1922E is
open drain with an internal circuit equivalent to that
shown in Figure 10.
A multidrop bus consists of a 1-Wire bus with multiple
slaves attached. At standard speed the 1-Wire bus has
a maximum data rate of 16.3kbps. The speed can be
boosted to 142kbps by activating the Overdrive Mode.
The DS1922E is not guaranteed to be fully compliant to
the iButton standard. Its maximum data rate in standard
speed is 15.4kbps and 125kbps in overdrive speed.
Figure 10. Hardware Configuration
High-Temperature Logger iButton with 8KB
Hardware Configuration
______________________________________________________________________________________
1-Wire Bus System
Rx
Tx
BUS MASTER
OPEN-DRAIN
PORT PIN
Tx = TRANSMIT
Rx = RECEIVE
V
PUP
R
PUP
The value of the pullup resistor primarily depends on
the network size and load conditions. The DS1922E
requires a pullup resistor of maximum 2.2kΩ at any
speed.
The idle state for the 1-Wire bus is high. If for any rea-
son a transaction needs to be suspended, the bus
must be left in the idle state if the transaction is to
resume. If this does not occur and the bus is left low for
more than 16µs (overdrive speed) or more than 120µs
(standard speed), one or more devices on the bus may
be reset. Note that the DS1922E does not quite meet
the full 16µs maximum low time of the normal 1-Wire
bus overdrive timing. With the DS1922E the bus must
be left low for no longer than 12µs at overdrive to
ensure that no DS1922E on the 1-Wire bus performs a
reset. The DS1922E communicates properly when used
in conjunction with a DS2480B or DS2490 1-Wire driver
and adapters that are based on these driver chips.
The protocol for accessing the DS1922E through the
1-Wire port is as follows:
• Initialization
• ROM Function Command
• Memory/Control Function Command
• Transaction/Data
DATA
I
L
DS1922E 1-Wire PORT
Data-Log Memory
100Ω MOSFET
Transaction Sequence
Rx
Tx
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