DS2506 查看數據表（PDF） - Dallas Semiconductor -> Maxim Integrated

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DS2506

64-kbit Add-Only Memory

Dallas Semiconductor -> Maxim Integrated 

DS2506

The next 32 bytes of the EPROM Status Memory (addresses 020 to 03FH) contain the Write Protect bits

which inhibit altering the Page Address Redirection Byte corresponding to each page in the 65536-bit

main memory area.

The following 32 bytes within the EPROM Status Memory (addresses 040 to 05FH) are reserved for use

by the iButton operating software TMEX. Their purpose is to indicate which memory pages are already in

use. Originally, all of these bits are unprogrammed, indicating that the device does not store any data. As

soon as data is written to any page of the device under control of TMEX, the bit inside this bitmap

corresponding to that page will be programmed to 0, marking this page as used. These bits are application

flags only and have no impact on the internal logic of the DS2506.

The next 256 bytes of the EPROM Status Memory (addresses 100H to 1FFH) contain the Page Address

Redirection Bytes which indicate if one or more of the pages of data in the 65536-bit EPROM section

have been invalidated by software and redirected to the page address contained in the appropriate

redirection byte. The hardware of the DS2506 makes no decisions based on the contents of the Page

Address Redirection Bytes. Since with EPROM technology bits can only be changed from a logical 1 to

a logical 0 by programming, 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

DS2506. Under TMEX a page is redirected 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. To leave an

authentic audit trail of data patches, it is recommended to also program the write protect bit of the Page

Address Redirection Byte, after the page redirection is programmed. Without this protection, it is still

possible to modify the Page Address Redirection Byte, making it point to a different memory page than

the true one.

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 than FFH, the data in the

page corresponding to that redirection byte is invalid. According to the TMEX definitions 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 status memory is programmed

similarly to the data memory. Details for reading and programming the EPROM status memory portion of

the DS2506 are given in the Memory Function Commands section.

The Status Memory address range of the DS2506 extends from 000 to 1FFH. The memory locations 60H

to 0FFH and 200H and higher are physically not implemented. Reading these locations will usually

result in FFH bytes. Attempts to write to these locations will be ignored.

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