DS2760
16
All transactions of the 1-Wire bus begin with an initialization sequence consisting of a Reset Pulse
transmitted by the bus master followed by a presence pulse simultaneously transmitted by the DS2760
and any other slaves on the bus. The presence pulse tells the bus master that one or more devices are on
the bus and ready to operate. For more details, see the
1-Wire Signaling section.
NET ADDRESS COMMANDS
Once the bus master has detected the presence of one or more slaves, it can issue one of the Net Address
Commands described in the following paragraphs. The name of each ROM Command is followed by the
8-bit opcode for that command in square brackets. Figure 16 presents a transaction flowchart of the Net
Address Commands.
Read Net Address [33h or 39h]. This command allows the bus master to read the DS2760’s 1-Wire net
address. This command can only be used if there is a single slave on the bus. If more than one slave is
present, a data collision occurs when all slaves try to transmit at the same time (open-drain produces a
wired-AND result). The RNAOP bit in the Status Register selects the opcode for this command, with
RNAOP=0 indicating 33h and RNAOP=1 indicating 39h.
Match Net Address [55h]. This command allows the bus master to specifically address one DS2760 on
the 1-Wire bus. Only the addressed DS2760 responds to any subsequent Function Command. All other
slave devices ignore the Function Command and wait for a reset pulse. This command can be used with
one or more slave devices on the bus.
Skip Net Address [CCh]. This command saves time when there is only one DS2760 on the bus by
allowing the bus master to issue a Function Command without specifying the address of the slave. If
more than one slave device is present on the bus, a subsequent Function Command can cause a data
collision when all slaves transmit data at the same time.
Search Net Address [F0h]. This command allows the bus master to use a process of elimination to
identify the 1-Wire net addresses of all slave devices on the bus. The search process involves the
repetition of a simple three-step routine: read a bit, read the complement of the bit, then write the desired
value of that bit. The bus master performs this simple three-step routine on each bit location of the net
address. After one complete pass through all 64 bits, the bus master knows the address of one device.
The remaining devices can then be identified on additional iterations of the process. See Chapter 5 of the
Book of DS19xx iButton
®
Standards for a comprehensive discussion of a net address search, including an
actual example. (This publication can be found on the Maxim/Dallas Semiconductor website at
www.maxim-ic.com).
SWAP [AAh]. SWAP is a Net Address level command specifically intended to aid in distributed
multiplexing applications and is described specifically with regards to power control using the 27xx series
of products. The term power control refers to the ability of the DS2760 to control the flow of power into
or out the battery pack using control pins
DC and CC . The SWAP command is issued followed by the
Net Address. The effect is to cause the addressed device to enable power to or from the system while
simultaneously (break-before-make) deselecting and powering down (SLEEP) all other packs. This
switching sequence is controlled by a timing pulse issued on the DQ line following the net address. The
falling edge of the pulse is used to disable power with the rising edge enabling power flow by the selected
device. The DS2760 will recognize a SWAP command, device address, and timing pulse if and only if
the SWEN bit is set.
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