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DS2704W Datasheet(PDF) 6 Page - Maxim Integrated Products |
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DS2704W Datasheet(HTML) 6 Page - Maxim Integrated Products |
6 / 18 page DS2704: 1280-Bit EEPROM with SHA-1 Authentication 6 of 18 Table 1. Authentication Function Commands COMMAND Hex FUNCTION Write Challenge 0C Writes 64-bit challenge for SHA-1 processing. Required prior to issuing Compute MAC and Compute Next Secret commands. Compute MAC without ROM ID and return MAC 36 Computes hash the message block with logical 1’s in place of the ROM ID. Returns the 160-bit MAC. Compute MAC with ROM ID and return MAC 35 Computes hash of the message block including the ROM ID. Returns the 160-bit MAC. SECRET MANAGEMENT FUNCTION COMMANDS CLEAR SECRET [5Ah]. This command sets the 64-bit secret to all 0’s (0000 0000 0000 0000h). The host must wait tEEC for the DS2704 to write the new secret value to EEPROM. See Figure 10 on page 18 for command timing. COMPUTE NEXT SECRET WITHOUT ROM ID [30h]. This command initiates a SHA-1 computation of the MAC and uses a portion of the resulting MAC as the next or new secret. The MAC computation is performed with the current 64-bit secret and the 64-bit challenge. Logical 1’s are loaded in place of the ROM ID. 64-bits of the output MAC are used as the new secret value. The host must allow tSHA after issuing this command for the SHA calculation to complete, then wait tEEC for the DS2704 to write the new secret value to EEPROM. See Figure 8 on page 17 for command timing. COMPUTE NEXT SECRET WITH ROM ID [33h]. This command initiates a SHA-1 computation of the MAC and uses a portion of the resulting MAC as the next or new secret. The MAC computation is performed with the current 64-bit secret, the 64-bit ROM ID and the 64-bit challenge. 64-bits of the output MAC are used as the new secret value. The host must allow tSHA after issuing this command for the SHA calculation to complete, then wait tEEC for the DS2704 to write the new secret value to EEPROM. See Figure 8 on page 17 for command timing. LOCK SECRET [6Ah]. This command write protects the 64-bit Secret to prevent accidental or malicious overwrite of the secret value. The Secret value stored in EEPROM becomes "final." The host must wait tEEC for the DS2704 to write the lock secret bit to EEPROM. See Figure 10 on page 18 for command timing. Table 2. Secret Loading Function Commands COMMAND Hex FUNCTION Clear Secret 5A Clears the 64-bit Secret to 0000 0000 0000 0000h Compute Next Secret without ROM ID 30 Generates new global secret Compute Next Secret with ROM ID 33 Generates new unique secret Lock Secret 6A Sets lock bit to prevent changes to the Secret 1-WIRE SPEED CONTROL FUNCTION COMMANDS CLEAR OVERDRIVE [8Dh]. This command selects the Standard 1-Wire timings shown in the Electrical Characteristics table. The setting is stored in EEPROM so that the programmed speed selection can be recalled on initial power up. The host must wait tEEC for the DS2704 to write the EEPROM. See Figure 10 for command timing. Standard 1-Wire timing is the factory default. SET OVERDRIVE [8Bh]. This command selects the Overdrive 1-Wire timings shown in the Electrical Characteristics table. The setting is stored in EEPROM so that the programmed speed selection can be recalled on initial power up. The host must wait tEEC for the DS2704 to write the EEPROM. See Figure 10 for command timing. |
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