DS1961S-F3 Maxim Integrated Products, DS1961S-F3 Datasheet - Page 9

• Manufacturer Part Number: DS1961S-F3
• Description: IBUTTON EEPROM 1KBit SHA-1 2CAN
• Manufacturer: Maxim Integrated Products
• Series: iButton®r

Specifications of DS1961S-F3

• Rohs Information: IButton RoHS Compliance Plan
• Memory Size: 128B
• Memory Type: EEPROM
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

DS1961S
Read Scratchpad [AAh]
The read scratchpad command allows verifying the target address and the integrity of the scratchpad data.
After issuing the command code, the master begins reading. The first two bytes is the target address with
T2 to T0 = 0. The next byte is the ending offset/data status byte (E/S) followed by the scratchpad data,
which may be different from what the master has originally sent. This is of particular importance if the
target address is the secret, the register page, page 1 (in EPROM mode), or if refresh was used to load the
scratchpad. In these cases, the scratchpad can contain data other than that which was sent during either
the write scratchpad or refresh scratchpad commands. The master should read through the end of the
scratchpad after which it receives the inverted CRC that is computed with the data as sent by the
DS1961S. If the master continues reading after the CRC all data is FFh.
The scratchpad can be loaded using the write scratchpad or refresh scratchpad command. The data found
in the scratchpad depends on the command used, the target address, and whether or not EPROM mode is
active. See the descriptions of write scratchpad and refresh scratchpad for clarification.
Load First Secret [5Ah]
The load first secret command has two modes of operation, which are controlled by the EN_LFS flag.
With EN_LFS = 0, the command replaces the device’s current secret with the contents of the scratchpad,
provided that the secret is not write-protected. With EN_LFS = 1, the command allows to rewrite
memory data (addresses 0000h to 007Fh), bypassing the SHA-1 computation that is required when doing
the same through the copy scratchpad command. The EN_LFS flag is 0 unless it has been set to 1 by
executing the refresh scratchpad command prior to load first secret.
Case EN_LFS = 0
Before the load first secret command can be used in this mode, the master must have written the new
secret to the scratchpad using the starting address of the secret (0080h). After issuing the load first secret
command, the master must provide a 3-byte authorization pattern (TA1, TA2, E/S, in that order), that
should have been obtained by an immediately preceding read scratchpad command. This 3-byte pattern
must exactly match the data contained in the three address registers (see Figure 6). If the pattern matches
and the secret is not write-protected, the AA flag is set and the copy begins. All eight bytes of scratchpad
contents are copied to the secret’s memory location.
Case EN_LFS = 1
To use the load first secret command in this mode, the refresh scratchpad command must have been
executed to load eight bytes of memory data (address range 0000h to 007Fh) into the scratchpad, which
sets the EN_LFS flag to 1. After issuing the load first secret command, the master must provide a 3-byte
authorization pattern (TA1, TA2, E/S, in that order), that can be obtained by an immediately preceding
read scratchpad command without affecting the EN_LFS flag. This 3-byte pattern must exactly match the
data contained in the three address registers (see Figure 6). If the pattern matches and the memory is not
write-protected, the AA flag is set and the copy begins. All eight bytes of scratchpad contents are copied
to the memory location.
Regardless of the mode used, the duration of the copy operation is t
during which the voltage on the
PROG
1-Wire bus must not fall below 2.8V. The master should read at least one byte at the conclusion of the
copy delay. Reading AAh indicates that the copy was successful, while reading FFh indicates that the
copy was not successful. Instead of using load first secret with EN_LFS = 0, a new secret can
alternatively be loaded with the copy scratchpad command. However, this approach requires the
knowledge of the current secret and the computation of a 160-bit MAC.
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