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DS1982 Datasheet

  • DS1982

  • UniqueWare iButtonTM

  • Dallas   Dallas

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DS1982
1024-BIT EPROM
The memory map in Figure 5 shows the 1024-bit EPROM section of the DS1982 which is configured as
four pages of 32 bytes each. The 8-bit scratchpad is an additional register that acts as a buffer when
programming the memory. Data is first written to the scratchpad and then verified by reading an 8-bit
CRC from the DS1982 that confirms proper receipt of the data. If the buffer contents are correct, a
programming voltage should be applied and the byte of data will be written into the selected address in
memory. This process ensures data integrity when programming the memory. The details for reading and
programming the 1024-bit EPROM portion of the DS1982 are given in the "Memory Function
Commands" section.
EPROM STATUS BYTES
In addition to the 1024 bits of data memory the DS1982 provides 64 bits of status memory accessible
with separate commands.
The EPROM Status Bytes can be read or programmed to indicate various conditions to the software
interrogating the DS1982. The first byte of the EPROM status memory contains the Write-Protect Page
bits which inhibit programming of the corresponding page in the 1024-bit main memory area if the
appropriate write protection bit is programmed. Once a bit has been programmed in the Write-Protect
Page byte, the entire 32-byte page that corresponds to that bit can no longer be altered but may still be
read.
The next 4 bytes of the EPROM Status Memory contain the Page Address Redirection Bytes which
indicate if one or more of the pages of data in the 1024-bit EPROM section have been invalidated and
redirected to the page address contained in the appropriate redirection byte. The hardware of the DS1982
makes no decisions based on the contents of the Page Address Redirection Bytes. These additional bytes
of status EPROM allow for the redirection of an entire page to another page address, indicating that the
data in the original page is no longer considered relevant or valid. With EPROM technology, bits within a
page can be changed from a logical 1 to a logical 0 by programming, but cannot be changed back.
Therefore, it is not possible to simply rewrite a page if the data requires changing or updating, but with
space permitting, an entire page of data can be redirected to another page within the DS1982 by writing
the one鈥檚 complement of the new page address into the Page Address Redirection Byte that corresponds
to the original (replaced) page.
This architecture allows the user鈥檚 software to make a 鈥渄ata patch鈥?to the EPROM by indicating that a
particular page or pages should be replaced with those indicated in the Page Address Redirection Bytes.
If a Page Address Redirection Byte has a FFH value, the data in the main memory that corresponds to that
page is valid. If a Page Address Redirection Byte has some other hex value, the data in the page
corresponding to that redirection byte is invalid, and the valid data can now be found at the one鈥檚
complement of the page address indicated by the hex value stored in the associated Page Address
Redirection Byte. A value of FDH in the redirection byte for page 1, for example, would indicate that the
updated data is now in page 2. The details for reading and programming the EPROM status memory
portion of the DS1982 is given in the Memory Function Commands section.
MEMORY FUNCTION COMMANDS
The 鈥淢emory Function Flow Chart鈥?(Figure 6) describes the protocols necessary for accessing the
various data fields within the DS1982. The Memory Function Control section, 8-bit scratchpad, and the
Program Voltage Detect circuit combine to interpret the commands issued by the bus master and create
the correct control signals within the device. A 3-byte protocol is issued by the bus master. It is comprised
of a command byte to determine the type of operation and 2 address bytes to determine the specific
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