ATSHA204 datasheet(32/65 Pages) ATMEL

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Atmel ATSHA204 [DATASHEET]

8740D

−CRYPTO−3/12

Commands

8.1

I/O Blocks

Regardless of the I/O protocol being used (single-wire or I

2C), commands are sent to the device, and responses received from

the device, within a block that is constructed in the following way:

Table 8-1.

I/O blocks

Byte #

Name

Meaning

Count

Number of bytes to be transferred to (or from) the device in the block, 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. Thus,

for a block with one count byte, 50 packet bytes, and two checksum bytes, the count byte should

be set to 53. The maximum size block (and value of count) is 84 bytes, and the minimum size

block is four bytes. Values outside this range will cause unpredictable operation.

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

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, and

so the last byte of the block is the most-significant byte of the CRC.

The ATSHA204 is designed in such a way that the count value in the input block should be consistent with the size

requirements specified in the command parameters. If the count value is inconsistent with the command opcode and/or

parameters within the packet, the ATSHA204 will respond in different ways, depending on the specific command. Either the

response may include an error indication or some input bytes may be silently ignored.

8.1.1

Command Packets

The command packet is broken down as shown in Table 8-2.

Table 8-2.

Command packets

Byte #

Name

Meaning

Opcode

The Command Code – see Section 8.1.4

Param1

The First Parameter – always present

2-3

Param2

The Second Parameter – always present

Data

Optional remaining input data

After the ATSHA204 receives all the bytes in a block, 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 device’s I/O interface

ignores all SDA transitions regardless of the I/O interface selected. The command execution delays are listed in Section 8.1.4.

If insufficient bytes are sent to the device when it is in one-wire mode, the device automatically transitions to the low-power

sleep state after the tTIMEOUT interval. In I

2C mode, the device continues to wait for the remaining bytes until the watchdog timer

limit, tWATCHDOG, is reached or a start/stop condition is received by the device.

In the individual command description tables below in Sections 8.2 through 8.13, the size column describes the number of

bytes in the parameter documented in each particular row. If the input block size for a particular command is incorrect, the

device does not attempt to execute the command; instead, the device returns an error.

ATSHA204 Datasheet(PDF) 32 Page - ATMEL Corporation

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