Rainbow Electronics DS2788 - Manual (Page 25)

Match Net Address [55h]. This command allows the
bus master to specifically address one DS2788 on the
1-Wire bus. Only the addressed DS2788 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 DS2788 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 func-
tion 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 comple-
ment 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 com-
plete 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
p r o c e s s . S e e C h a p t e r 5 o f t h e B o o k o f i B u t t o n
Standards for a comprehensive discussion of a net
a d d r e s s s e a r c h , i n c l u d i n g a n a c t u a l e x a m p l e
( www.maxim-ic.com/ibuttonbook ).
Resume [A5h]. This command increases data through-
put in multidrop environments where the DS2788 needs
to be accessed several times. Resume is similar to the
Skip Net Address command in that the 64-bit net
address does not have to be transmitted each time the
DS2788 is accessed. After successfully executing a
Match Net Address command or Search Net Address
command, an internal flag is set in the DS2788. When
the flag is set, the DS2788 can be repeatedly accessed
through the Resume command function. Accessing
another device on the bus clears the flag, thus prevent-
ing two or more devices from simultaneously respond-
ing to the Resume command function.
Function Commands
After successfully completing one of the net address
commands, the bus master can access the features of
t h e D S 2 7 8 8 w i t h a n y o f t h e f u n c t i o n c o m m a n d s
described in the following paragraphs. The name of
each function is followed by the 8-bit op code for that
command in square brackets. Table 5 summarizes the
function commands.
Read Data [69h, XX]. This command reads data from
the DS2788 starting at memory address XX. The LSb of
the data in address XX is available to be read immedi-
ately after the MSb of the address has been entered.
Because the address is automatically incremented after
the MSb of each byte is received, the LSb of the data at
address XX + 1 is available to be read immediately
after the MSb of the data at address XX. If the bus mas-
ter continues to read beyond address FFh, data is read
starting at memory address 00 and the address is auto-
matically incremented until a reset pulse occurs.
Addresses labeled “Reserved” in the memory map
contain undefined data values. The read data com-
mand can be terminated by the bus master with a reset
pulse at any bit boundary. Reads from EEPROM block
addresses return the data in the shadow RAM. A Recall
Data command is required to transfer data from the
EEPROM to the shadow. See the Memory section for
more details.
Write Data [6Ch, XX]. This command writes data to the
DS2788 starting at memory address XX. The LSb of the
data to be stored at address XX can be written immedi-
ately after the MSb of address has been entered.
Because the address is automatically incremented after
the MSb of each byte is written, the LSb to be stored at
address XX + 1 can be written immediately after the
MSb to be stored at address XX. If the bus master con-
tinues to write beyond address FFh, the data starting at
address 00 is overwritten. Writes to read-only address-
es, reserved addresses, and locked EEPROM blocks
are ignored. Incomplete bytes are not written. Writes to
unlocked EEPROM block addresses modify the shad-
ow RAM. A Copy Data command is required to transfer
data from the shadow to the EEPROM. See the Memory
section for more details.
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Stand-Alone Fuel-Gauge IC with
LED Display Drivers
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