DS2407 Dallas Semiconducotr, DS2407 Datasheet - Page 3

• Manufacturer Part Number: DS2407
• Description: Dual Addressable Switch Plus 1K.Bit Memory
• Manufacturer: Dallas Semiconducotr

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 X
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).
8
+ X
5
+ X
4
+ 1. Additional information
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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DS2407