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DS2407V Datasheet(PDF) 3 Page - Dallas Semiconductor |
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DS2407V Datasheet(HTML) 3 Page - Dallas Semiconductor |
3 / 31 page DS2407 012099 3/31 64–BIT LASERED ROM Each DS2407 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 1–Wire CRC of the lasered ROM is generated using the polynomial X8 + X5 + X4 + 1. Additional information about the Dallas Semiconductor 1–Wire Cyclic Redun- dancy Check is available in the Book of DS19xx iButton Standards. The 64–bit ROM and ROM Function Control section allow the DS2407 to operate as a 1–Wire device and follow the 1–Wire protocol detailed in the section “1–Wire Bus System”. The functions required to read and write the data and status memory of the DS2407 and to access the switches are not accessible until the ROM function protocol has been satisfied. This protocol is described in the ROM func- tions flow chart (Figure 12). The 1–Wire bus master must first provide one of the five ROM function com- mands. After a ROM function sequence has been suc- cessfully executed, the bus master may then provide any one of the memory function commands specific to the DS2407 (Figure 6). MEMORY The DS2407 contains two memory sections, Data Memory and Status Memory. The data memory consists of 1024 bits of one–time programmable EPROM orga- nized as 4 pages of 32 bytes each. The size of the device’s status memory is 8 bytes. The first seven bytes of status memory (addresses 0 to 6) are also realized as EPROM. The eighth byte (address 7) consists of SRAM cells which shadow the contents of address 6 each time the device powers up. The complete memory map is shown in Figure 4. The 8–bit scratchpad is an additional register that acts as a buffer when writing the memory. Data is first written to the scratchpad and then verified by reading a 16–bit CRC from the DS2407 that confirms proper receipt of the data and address. If the buffer con- tents are correct, a programming pulse should be applied and the byte of data will be written into the selected address in memory. This process insures data integrity when programming the memory. The details for reading and programming the EPROM portions of the DS2407 are given in the Memory Function Commands section. |
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