DS1990R-F3# Maxim Integrated Products, DS1990R-F3# Datasheet - Page 6

• Manufacturer Part Number: DS1990R-F3#
• Description: IBUTTON SERIAL NUMBER F3
• Manufacturer: Maxim Integrated Products
• Series: iButton®r

Specifications of DS1990R-F3#

• Rohs Information: IButton RoHS Compliance Plan
• Memory Size: 8B
• Memory Type: ROM
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Serial Number iButton
Figure 5. ROM Functions Flowchart
6
FUNCTION COMMAND
BUS MASTER Tx ROM
_______________________________________________________________________________________
SERIAL NUMBER
0Fh READ ROM
FAMILY CODE
COMMAND?
DS1990R Tx
DS1990R Tx
DS1990R Tx
CRC BYTE
(6 BYTES)
(1 BYTE)
33h OR
Y
N
PRESENCE PULSE
BUS MASTER Tx
RESET PULSE
DS1990R Tx
N
N
N
DS1990R Tx BIT 63
DS1990R Tx BIT 63
MASTER Tx BIT 63
DS1990R Tx BIT 0
DS1990R Tx BIT 0
DS1990R Tx BIT 1
DS1990R Tx BIT 1
MASTER Tx BIT 0
MASTER Tx BIT 1
BIT 63 MATCH?
BIT 0 MATCH?
BIT 1 MATCH?
SEARCH ROM
COMMAND?
F0h
Y
Y
Y
Y
N
Once the bus master has detected a presence pulse, it
can issue one of the ROM function commands the
DS1990R supports. All ROM function commands are
8 bits long. A list of these commands follows. (See
Figure 5 for a flowchart.)
This command allows the bus master to read the
DS1990R’s 8-bit family code, unique 48-bit serial num-
ber, and 8-bit CRC. This command can only be used if
there is a single slave device on the bus. If more than one
slave is present on the bus, a data collision occurs when
all slaves try to transmit at the same time (open drain pro-
duces a wired-AND result). The resultant family code and
48-bit serial number results in a mismatch of the CRC.
When a system is initially brought up, the bus master
might not know the number of devices on the 1-Wire
bus or their registration numbers. By taking advantage
of the wired-AND property of the bus, the master can
use a process of elimination to identify the registration
numbers of all slave devices. For each bit of the regis-
tration number, starting with the least significant bit, the
bus master issues a triplet of time slots. On the first slot,
each slave device participating in the search outputs
the true value of its registration number bit. On the sec-
ond slot, each slave device participating in the search
outputs the complemented value of its registration num-
ber bit. On the third slot, the master writes the true
value of the bit to be selected. All slave devices that do
not match the bit written by the master stop participat-
ing in the search. If both of the read bits are zero, the
master knows that slave devices exist with both states
of the bit. By choosing which state to write, the bus
master branches in the ROM code tree. After one com-
plete pass, the bus master knows the registration num-
ber of a single device. Additional passes identify the
registration numbers of the remaining devices. Refer to
Application Note 187: 1-Wire Search Algorithm for a
detailed discussion, including an example.
The minimum set of 1-Wire ROM function commands
includes a Match ROM and a Skip ROM command.
Because the DS1990R contains only the 64-bit ROM
without any additional data fields, Match ROM and Skip
ROM are not applicable. The DS1990R remains silent
(inactive) upon receiving a ROM function command
that it does not support. This allows the DS1990R to
coexist on a multidrop bus with other 1-Wire devices
that do respond to Match ROM or Skip ROM.
1-Wire ROM Function Commands
Match ROM [55h]/Skip ROM [CCh]
Read ROM [33h] or [0Fh]
Search ROM [F0h]