DS2432X Dallas Semiconducotr, DS2432X Datasheet - Page 17

• Manufacturer Part Number: DS2432X
• Description: 1k-Bit Protected 1-Wire EEPROM with SHA-1 Engine
• Manufacturer: Dallas Semiconducotr

PRELIMINARY
Special attention is required when copying data to the register page. In order to prevent unintentional
locking of a special function register or user byte it is recommended to first read the register page and
then write it all with the intended modification to the scratchpad. When writing to the register page (or the
secret using Copy Scratchpad), the input data for M1 to M7 of the SHA engine will be the current secret
(M1, M2), the current content of the register page (M3, M4), the full 64-bit registration number (M5,
M6), and 4 bytes FFh (M7).
SHA-1 Input Data for Copy Scratchpad Command Table 3
Legend
Read Authenticated Page [A5h]
The Read Authenticated Page command provides the master with the data of a full or partial memory
page plus a message authentication code (MAC). The MAC allows the master to determine whether the
secret stored in the DS2432 is valid within the application. The DS2432 computes the MAC from its
secret, all the data of the selected memory page, its registration number and a 3-byte challenge, which the
master should write to the scratchpad prior to issuing the Read Authenticated Page command. To do this,
the master can use the write scratchpad command with any target address within the data memory. The
relevant portions of the challenge are the 5
M0[31:24] = (SS+0)
M1[31:24] = (PP+0)
M2[31:24] = (PP+4)
M3[31:24] = (PP+8)
M4[31:24] = (PP+12)
M5[31:24] = (PP+16)
M6[31:24] = (PP+20)
M7[31:24] = (PP+24)
M8[31:24] = (SP+0)
M9[31:24] = (SP+4)
M10[31:24] = MP
M11[31:24] = SN2
M12[31:24] = (SS+4)
M13[31:24] = FFh
M14[31:24] = 00h
M15[31:24] = 00h
Mt
SS
PP
(SP+n)
MP
FAMC
SNx
M4[23:16] = (PP+13)
M5[23:16] = (PP+17)
M6[23:16] = (PP+21)
M7[23:16] = (PP+25)
M11[23:16] = SN3
M12[23:16] = (SS+5)
M0[23:16] = (SS+1)
M1[23:16] = (PP+1)
M2[23:16] = (PP+5)
M3[23:16] = (PP+9)
M8[23:16] = (SP+1)
M9[23:16] = (SP+5)
M10[23:16] = FAMC
M13[23:16] = FFh
M14[23:16] = 00h
M15[23:16] = 00h
Input buffer of SHA engine
0 t
Starting address of secret (80h)
Starting address of memory page
See Memory Map, memory pages 0 through 3
Byte n of scratchpad
MP[7:4] = 0000 for Copy Scratchpad
MP[3:0] = T8:T5 (equivalent to page number in hex)
Family Code = 33h
Serial number of device
SN0 = least significant byte, SN5 = most significant byte.
The CRC is not used
15; 32-bit words
th
, 6
th
and 7
17 of 30
M0[15:8] = (SS+2)
M1[15:8] = (PP+2)
M2[15:8] = (PP+6)
M3[15:8] = (PP+10)
M4[15:8] = (PP+14)
M5[15:8] = (PP+18)
M6[15:8] = (PP+22)
M7[15:8] = (PP+26)
M8[15:8] = (SP+2)
M9[15:8] = (SP+6)
M10[15:8] = SN0
M11[15:8] = SN4
M12[15:8] = (SS+6)
M13[15:8] = FFh
M14[15:8] = 00h
M15[15:8] = 01h
th
byte. Alternatively, the master can accept the data
M0[7:0] = (SS+3)
M1[7:0] = (PP+3)
M2[7:0] = (PP+7)
M3[7:0] = (PP+11)
M4[7:0] = (PP+15)
M5[7:0] = (PP+19)
M6[7:0] = (PP+23)
M7[7:0] = (PP+27)
M8[7:0] = (SP+3)
M9[7:0] = (SP+7)
M10[7:0] = SN1
M11[7:0] = SN5
M12[7:0] = (SS+7)
M13[7:0] = 80h
M14[7:0] = 00h
M15[7:0] = B8h
DS2432