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DS1982 Datasheet(PDF) 6 Page - Dallas Semiconductor |
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DS1982 Datasheet(HTML) 6 Page - Dallas Semiconductor |
6 / 23 page DS1982 6 of 23 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’s complement of the new page address into the Page Address Redirection Byte that corresponds to the original (replaced) page. This architecture allows the user’s software to make a “data patch” 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’s 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 “Memory Function Flow Chart” (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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