ATECC508A datasheet(55/109 Pages) MICROCHIP

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Security Commands

9.1

I/O Groups

Regardless of the I/O protocol being used (i.e. either Single-Wire Interface or I2C); security commands

are sent to the device and responses received from the device within a group that is constructed in the

following way:

Table 9-1. I/O Groups

Byte

Name

Meaning

Count

Number of bytes to be transferred to (or from) the device in the group, including count byte,

packet bytes, and checksum bytes. The count byte should therefore always have a value of

(N+1), where N is equal to the number of bytes in the packet plus the two checksum bytes.

For a group with one count byte, 50 packet bytes, and two checksum bytes, the count byte

should be set to 53. The maximum size group (and value of count) is 155 bytes, and the

minimum size group is four bytes. Values outside this range will cause the device to return

an I/O Error.

1 to

(N-2)

Packet

Command, parameters and data, or response. See below for more details.

N-1, N

Checksum CRC-16 verification of the count and packet bytes. The CRC polynomial is 0x8005. The

initial register value should be zero and after the last bit of the count and packet have been

transmitted, the internal CRC register should have a value that matches the checksum bytes

in the block. The first CRC byte transmitted (N-1) is the least-significant byte of the CRC

value, so the last byte of the group is the most-significant byte of the CRC.

The ATECC508A is designed in such a way that the count value in the input group should be consistent

with the size requirements that are specified in the command parameters. If the count value is

inconsistent with the command opcode and/or parameters within the packet, then the ATECC508A will

respond in different ways depending upon the specific command. The response may either include an

error indication or some input bytes may be silently ignored.

9.1.1

Security Command Packets

The security command packet is broken down as shown in the table below:

Table 9-2. Security Command Packets

Byte

Name

Meaning

Opcode The command code. See Section Command Opcodes, Short Descriptions, and Execution Times.

Param1 The first parameter; always present.

2 – 3 Param2 The second parameter; always present.

Data

Optional remaining input data.

After the ATECC508A receives all the bytes in a group, the device transitions to the busy state and

attempts to execute the command. Neither status nor results can be read from the device when it is busy.

During this time, the I/O interface of the device ignores all SDA transitions regardless of the I/O interface

selected. The command execution delays are listed in Section Command Opcodes, Short Descriptions,

and Execution Times.

ATECC508A

Security Commands

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