DS28EC20: 20Kb 1-Wire EEPROM
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Figure 4. 1-Wire CRC Generator
Polynomial = X
8
+ X
5
+ X
4
+ 1
MEMORY
Data memory and special function registers are located in a linear address space, as shown in Figure 5. The data
memory and the registers have unrestricted read access. The data memory consists of 80 pages of 32 bytes each.
Eight adjacent pages form one 2Kb block. Each block can be individually set to open (default), write protected, or
EPROM mode by setting the associated protection byte in the register page, which starts at address 0A00h.
Besides the 10 block protection control bytes (one for each 2Kb data memory block) the register page contains 20
bytes of user EEPROM plus a memory block lock byte and a register page lock byte. Starting at address 0A20h,
the DS28EC20 has a read-only memory page that stores a factory byte and a 2-byte field reserved for a factory-
administered service to program manufacturer identification. All other bytes of that page are reserved. The
manufacturer ID can be a customer-supplied identification code that assists the application software in identifying
the product the DS28EC20 is associated with. Contact the factory to set up and register a custom manufacturer ID.
In addition to the EEPROM, the device has a 32-byte volatile scratchpad. Writes to the EEPROM array are a two-
step process. First, data is written to the scratchpad, and then copied into the main array. The user can verify the
data in the scratchpad prior to copying.
The protection control registers, along with the Memory Block Lock byte, determine whether write protection,
EPROM mode, or copy protection is enabled for each of the 10 data memory blocks. A value of 55h sets write
protection for the associated memory block. A value of AAh sets EPROM mode. The Memory Block Lock byte, if
programmed to either 55h or AAh, sets copy protection for all write-protected data memory blocks. Blocks in
EPROM mode are not affected. Programming the Register Page Lock byte to either 55h or AAh copy protects the
entire register page. The protection control registers and the Lock bytes write protect themselves if set to 55h or
AAh. Any other setting leaves them open for unrestricted write access. See the Copy Protection section for
explanation of copy protect vs. write protect.
Write Protection: Write protection prevents data from being changed, but does not block the copy-scratchpad
function; this allows the memory to be reprogrammed with the same data. In EEPROM devices digital information
is stored as electrical charge (electrons) on floating gates. Quantum mechanical effects allow electrons to be
transported in large numbers to and from the floating gate for programming and erasing memory cells. Electrons
leave the floating gate at a temperature-dependent rate. The higher the temperature, the faster is the rate at which
electrons escape. This rate is expressed as Data Retention in the EC table. Reprogramming the memory returns
the charge to the original value for a full data retention time. This is particularly useful in applications where data
retention is a concern, e.g., at high temperatures.
Copy Protection: Copy protection blocks the execution of the copy-scratchpad function. This feature achieves a
higher level of security, and should only be used after all write-protected locations and their associated protection
control bytes are set to their final values. Copy protection does not prevent copying data from one device to
another.
