DS1985

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Figure 8. After a ROM Function Command is successfully executed, the memory functions that operate

on the EPROM portions of the DS1985 become accessible and the bus master may issue any one of the

five Memory Function Commands specific to the DS1985 to read or program the various data fields. The

protocol for these Memory Function Commands is described in Figure 5. All data is read and written least

significant bit first.

DS1985 BLOCK DIAGRAM Figure 1

64-BIT LASERED ROM

Each DS1985 contains a unique ROM code that is 64 bits long. The first 8 bits are a 1-Wire family code.

The next 48 bits are a unique serial number. The last 8 bits are a CRC of the first 56 bits. (See Figure 3.)

The 64-bit ROM and ROM Function Control section allow the DS1985 to operate as a 1-Wire device and

follow the 1-Wire protocol detailed in the section “1-Wire Bus System.” The memory functions required

to read and program the EPROM sections of the DS1985 are not accessible until the ROM function

protocol has been satisfied. This protocol is described in the ROM functions flow chart (Figure 8). The 1-

Wire bus master must first provide one of four ROM function commands: 1) Read ROM, 2) Match ROM,

3) Search ROM, or 4) Skip ROM. After a ROM function sequence has been successfully executed, the

bus master may then provide any one of the memory function commands specific to the DS1985 (Figure

5).