DS1961S
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The secret can be installed either by copying data from the scratchpad to the secrets memory or by
computation using the current secret and the scratchpad contents as partial secret. The secret cannot be
read directly; only the SHA engine has access to it for computing message authentication codes.
The address range 0088h to 008Fh, also referred to as the Register Page, contains special function
registers as well as general-purpose user-bytes and one factory byte. Once programmed to AAh or 55h,
most of these bytes become write-protected and can no longer be altered. All other codes neither write-
protect the address nor activate the special function associated to that particular byte. Special functions
are: 1) write-protecting only the secret, 2) write-protecting all four data memory pages simultaneously, 3)
activating EPROM mode for data memory page 1 only, and 4) write-protecting data memory page 0 only.
Once EPROM mode is activated, bits in the address range 0020h through 003Fh can only be altered from
a logic 1 to a logic 0, provided that the data memory is not write protected.
The factory byte either reads 55H or AAh. Typically, this address reads 55h, indicating that the addresses
008E and 008F are read/write user-bytes without any special function or locking mechanism. The code of
AAh indicates that these two bytes are programmed with a 16-bit manufacturer ID and then write-
protected at the factory. The manufacturer ID can be a customer-supplied identification code that assists
the application software in identifying the product the DS1961S is associated with and in faster selection
of the applicable secret. To setup and register a manufacturer ID contact the factory.
The address range 0090h to 0097h is called the identity register. Typically, the identity register contains a
copy of the device’s ROM registration number. The family code is stored at the lower address followed
by the 48-bit serial number and the 8-bit CRC, which is stored at address 0097h. In reading through these
addresses (0090h to 0097h) the bus master receives the individual bits of the registration number in
exactly the same sequence as with a ROM function command. With customized versions, the content of
the identity register can be any customer-specified constant pattern. For more information on
customization contact the factory.
Figure 6. ADDRESS REGISTERS
Bit Number76543210
Target Address (TA1) T7 T6 T5 T4 T3
T2
(0)
T1
(0)
T0
(0)
Target Address (TA2) T15 T14 T13 T12 T11 T10 T9 T8
Ending Address with
Data Status (E/S)
(Read Only)
AA 1 PF 1 1
E2
(1)
E1
(1)
E0
(1)
ADDRESS REGISTERS AND TRANSFER STATUS
The DS1961S employs three address registers: TA1, TA2, and E/S (Figure 6). These registers are
common to many other 1-Wire devices but operate slightly differently with the DS1961S. Registers TA1
and TA2 must be loaded with the target address to which the data is written or from which data is read.
Register E/S is a read-only transfer-status register, used to verify data integrity with write commands.
Since the scratchpad of the DS1961S is designed to accept data in blocks of eight bytes only, the lower
three bits of TA1 are forced to 0 and the lower three bits of the E/S register (ending offset) always read 1.
