DS1986

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Function Commands is described in Figure 8. After a ROM Function Command is successfully executed,

the memory functions that operate on the EPROM portions of the DS1986 become accessible and the bus

master may issue any one of the five Memory Function Commands specific to the DS1986 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.

64-BIT LASERED ROM

Each DS1986 contains a unique ROM code that is 64 bits long. The first eight bits are a 1-Wire family

code. The next 48 bits are a unique serial number. The last eight bits are a CRC of the first 56 bits. (See

Figure 3.) The 64-bit ROM and ROM Function Control section allow the DS1986 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 DS1986 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 six ROM function commands: 1) Read ROM,

2) Match ROM, 3) Search ROM, or 4) Skip ROM, 5) Overdrive-Skip ROM, or 6) Overdrive-Match

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 DS1986 (Figure 5).

information about the Dallas Semiconductor 1-Wire Cyclic Redundancy Check is available in the Book

of DS19xx iButton Standards. The shift register acting as the CRC accumulator is initialized to zero.

Then starting with the least significant bit of the family code, one bit at a time is shifted in. After the

eighth bit of the family code has been entered, then the serial number is entered. After the 48th bit of the

serial number has been entered, the shift register contains the CRC value. Shifting in the eight bits of

CRC should return the shift register to all zeroes.