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DS2770

Battery Monitor and Charge Controller

Maxim Integrated 

DS2770

Skip Net Address [CCh]. This command saves time when there is only one DS2770 on the bus by

allowing the bus master to issue a Function command without specifying the net 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 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 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 passes. See Chapter 5 of The Book of DS19xx iButton Standards for a

comprehensive discussion of a net address search, including an actual example. The Search Net Address

algorithm cannot be used with the DS2770 in multi-drop applications with any 1-Wire devices that have

either a 6h or Eh as the LS byte of the 1-Wire family code. Because the 1-Wire family code of the

DS2770 is 2Eh, Search Net Address cannot be used to ascertain the 64-bit serial numbers of multiple

DS2770’s on a single bus. If an application does require two DS2770 to share a common bus, the bus

master may determine the serial numbers of each device using the Read Net Address function, with one

part configured to respond to the 33h command (RNAOP = 0) and the other the 39h command (RNAOP

= 1).

Resume [A5h]. This command is used to speed data throughput in multidrop environments where the

DS2770 needs to be accessed several times. The DS2770 contains an internal flag that, when set, directly

transfers control to the memory function commands upon receipt of a Resume command, similar to the

Skip Net Address command. The only way the internal flag is set is through successfully executing the

Match Net Address command or Search Net Address command. Once the flag is set, the device can

repeatedly be accessed through the Resume command function. Accessing another device on the bus will

clear the flag, thus preventing two or more devices from simultaneously responding to the Resume

command function.

FUNCTION COMMANDS

After successfully completing one of the five Net Address commands, the bus master can access the

features of the DS2770 with any of the Function commands described in the following paragraphs. The

name of each function is followed by the 8-bit opcode for that command in square brackets.

Read Data [69h, XX]. This command reads data from the DS2770 starting at memory address XX. The

LSb of the data in address XX is available to be read immediately 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 master continues to read beyond address FFh, the DS2770 will start over at address 00h.

Addresses labeled “reserved” in the memory map contain undefined data. The Read Data command may

be terminated by the bus master with a reset pulse at any bit boundary.

iButton is a registered trademark of Dallas Semiconductor.

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