DS1922T-F5# Maxim Integrated Products, DS1922T-F5# Datasheet - Page 36

• Manufacturer Part Number: DS1922T-F5#
• Description: IBUTTON TEMP LOGGER
• Manufacturer: Maxim Integrated Products
• Series: iButton®r

Specifications of DS1922T-F5#

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

Temperature Logger iButton with 8KB
Data-Log Memory
The 1-Wire bus is a system that has a single bus master
and one or more slaves. In all instances the
DS1922L/DS1922T are slave devices. The bus master
is typically a microcontroller. The discussion of this bus
system is broken down into three topics: hardware con-
figuration, transaction sequence, and 1-Wire signaling
(signal types and timing). The 1-Wire protocol defines
bus transactions in terms of the bus state during specif-
ic 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 DS1922L/
DS1922T is open drain with an internal circuit equiva-
lent 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 DS1922L/DS1922T are not guaranteed to
be fully compliant to the iButton standard. Their maxi-
mum data rate in standard speed is 15.4kbps and
125kbps in overdrive speed. The value of the pullup
Figure 10. Hardware Configuration
36
______________________________________________________________________________________
Hardware Configuration
Rx
1-Wire Bus System
Tx
BUS MASTER
OPEN-DRAIN
PORT PIN
Tx = TRANSMIT
Rx = RECEIVE
V
PUP
R
PUP
resistor primarily depends on the network size and
load conditions. The DS1922L/DS1922T require 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 DS1922L/DS1922T do not quite
meet the full 16µs maximum low time of the normal
1-Wire bus overdrive timing. With the DS1922L/
DS1922T, the bus must be left low for no longer than
12µs at overdrive to ensure that no DS1922L/DS1922T
on the 1-Wire bus performs a reset. The DS1922L/
DS1922T communicate properly when used in conjunc-
tion with a DS2480B or DS2490 1-Wire driver and
adapters that are based on these driver chips.
The protocol for accessing the DS1922L/DS1922T
through the 1-Wire port is as follows:
• Initialization
• ROM Function Command
• Memory/Control Function Command
• Transaction/Data
DATA
I
L
DS1922L/DS1922T 1-Wire PORT
100Ω MOSFET
Transaction Sequence
Rx
Tx