DS1977-F5 Просмотр технического описания (PDF) - Dallas Semiconductor -> Maxim Integrated

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DS1977-F5

32KB EEPROM iButton

Dallas Semiconductor -> Maxim Integrated 

The memory address range of the DS1977 iButton is 0000h to 7FFFh (see Figure ??). There is no

user-access to the address range 7FD1h to 7FFFh. If the 1-Wire master sends a target address

higher than this, the internal circuitry of the chip will set the most significant address bit to zero as

it is shifted into the internal address register. The Read Scratchpad command will reveal the

target address as it will be used by the DS1977 iButton. The 1-Wire master will identify such

address modifications by comparing the target address read back to the target address

transmitted. If the 1-Wire master does not read the scratchpad, a subsequent copy scratchpad

command will not work since the most significant bits of the target address the 1-Wire master

sends will not match the value the DS1977 iButton expects.

Read Scratchpad Command [AAh]

This command is used to verify scratchpad data and target address. After issuing the read

scratchpad command, the 1-Wire master begins reading. The first two bytes will be the target

address. The next byte will be the ending offset/data status byte (E/S) followed by the scratchpad

data beginning at the byte offset (T5: T0). The 1-Wire master may read data until the end of the

scratchpad. If the master generates additional times slots, it will read a CRC16 of the command

code, target address, E/S byte and scratchpad data starting at the byte offset, which is determined

by the target address.

Copy Scratchpad with Password [99h]

This command is used to copy data from the scratchpad to memory. After issuing the copy

scratchpad command, the 1-Wire master must provide a 3-byte authorization pattern, which can

be obtained by reading the scratchpad for verification. This pattern must exactly match the data

contained in the three address registers (TA1, TA2, E/S, in that order). Next the master must send

a valid write access password, or, if passwords are not enabled, 8 dummy bytes. Now the master

must provide power by bypassing the 1-Wire pull-up resistor with an electronic switch, generating

a "strong pull-up". If authorization pattern and password are accepted, the AA (Authorization

Accepted) flag will be set and the copy will begin. Copy takes 10ms maximum during which the

voltage on the 1-Wire bus must not fall below 2.8V. After the copy is completed, the master turns

off the strong pull-up and begins reading from the 1-Wire. A pattern of alternating 1’s and 0’s will

indicate that the copy command was executed successfully. If the copy command was disturbed

due to lack of power or for other reasons, the master will read a constant stream of FFh bytes until

it sends a 1-Wire reset pulse.

The data to be copied is determined by the three address registers (TA1, TA2, E/S). The

scratchpad data from the beginning offset through the ending offset will be copied to memory,

starting at the target address. Anywhere from 1 to 64 bytes may be copied to memory with this

command. When updating a password, instead of the password written to the scratchpad a

scrambled password is written to the memory location of the respective password.

After the DS1977 has received the password, the 1-Wire master must activate the strong pull-up.

Read Memory with Password [69h]

The read memory command may be used to read the entire memory, except for the passwords.

After issuing the command, the master must provide the 2-byte target address. Next the master

must send a valid read access password, or, if passwords are not enabled, 8 dummy bytes. Now

the master must provide power by bypassing the 1-Wire pull-up resistor with an electronic switch,

generating a "strong pull-up". If the password was accepted, EEPROM data beginning at the

specified target address and ending at the page boundary will be loaded into the scratchpad

starting at the beginning offset. This transfer takes 5 ms maximum during which the voltage on

the 1-Wire bus must not fall below 2.8V. After the transfer is completed, the master turns off the

strong pull-up and begins reading from the 1-Wire. When the end of the memory page (end of

scratchpad) is reached, the master will receive a CRC16 of the command, target address and

page data. If the master wants to read more data and the end of the memory is not yet reached, it

again has to activate the strong pull-up. This will transfer a full 64-byte page of memory data to

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1/31/03

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