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Atmel ATSHA204 [DATASHEET]

8740D

−CRYPTO−3/12

8.12

Read Command

Reads words (one 4-byte word or an 8-word block of 32 bytes) from one of the memory zones of the device. The data may

optionally be encrypted before being returned to the system. See also Section 8.1.5, “Zone Encoding,” and Section 8.1.4,

“Address Encoding,” for data zone byte and word addressing information.

If reading from a slot in which SlotConfig.EncryptRead is set, the GenDig command must have been run prior to the execution

of this command to generate the key that will be used for encryption. The input nonce to GenDig must have been a random

number, and the key specified in SlotConfig.ReadKey must have been used in the GenDig calculation.

The device encrypts data to be read by XORing each byte read from the EEPROM with the corresponding byte from

TempKey. Encrypted reads of the configuration and/or OTP zones are not permitted.

The byte addresses to be read should be divided by four (drop the least-significant two bits) before being passed to the device.

If 32 bytes are being read, the least-significant three bits of the input address are ignored. Addresses beyond the end of the

specified zone result in an error.

The following restrictions apply to the three zones:

Config

The words within this zone are always readable using this command, regardless of the value of LockConfig.

See Section 2.1.1, as some bytes are unreadable under any circumstances, and any attempt to read these

bytes result in an error.

OTP

If the OTP zone is unlocked, this command returns an error. Once locked, if OTPmode is set to a non-zero

value and the address points to either word zero or one, then the command also returns an error. Otherwise,

the corresponding word within the OTP zone is returned in the clear. If OTPmode is Legacy, then only four

byte reads are permitted.

Data

If the data zone is unlocked, this command returns an error. Otherwise, the values within the corresponding

SlotConfig word control access to the data slot. If SlotConfig.IsSecret is set and a four byte read is

attempted, the device returns an error. If EncryptRead is set, this command encrypts the data as specified

above. If IsSecret is set and EncryptRead is clear, this command returns an error. If IsSecret is clear and

EncryptRead is clear, this command returns the desired slot in the clear.

Table 8-33. Input Parameters

Name

Size

Notes

Opcode

READ

0x02

Param1

Zone

Bits 0 and 1: Select among config, OTP, or data. See Section 8.1.5.

Bits 2-6: Must be zero.

Bit 7: If one, 32 bytes are read; otherwise four bytes are read. Must be zero if reading from

OTP zone.

Param2

Address

Address of first word to be read within the zone. See Section 8.1.4.

Data

Table 8-34. Output Parameter

Name

Size

Notes

Contents

4 or 32

The contents of the specified memory location.

ATSHA204 Datasheet(PDF) 52 Page - ATMEL Corporation

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