ATSHA204A datasheet(31/93 Pages) MICROCHIP

31 / 93 page

ATSHA204A

I2C Name

Direction Description

7 of the I2C_Address byte in the Configuration zone. Bit 0 of this byte is

the standard I2C R/W bit and should be zero to indicate a Write

operation (the bytes following the device address travel from the master

to the slave).

Data

Data1,N

To Slave

The input block.

Because the device treats the command input buffer as a FIFO, the input block can be sent to the device

in one or many I2C command blocks. The first byte sent to the device is the count, so after the device

receives that number of bytes, it ignores any subsequently received bytes until execution is finished.

The system must send a Stop condition after the last command byte to ensure that the ATSHA204A

starts the computation of the command. Failure to send a Stop condition can eventually result in a loss of

synchronization (See Section I2C Synchronization for recovery procedures).

6.2.1

Word Address Values

During an I2C write packet, the ATSHA204A interprets the second byte sent as the word address, which

indicates the packet function, as described in the table below.

Table 6-2. Word Address Values

Name

Value

Description

Reset

0x00

Reset the address counter. The next read or write transaction starts with the

beginning of the I/O buffer.

Sleep

(Low Power)

0x01

The ATSHA204A goes into the low-power sleep mode and ignores all

subsequent I/O transitions until the next Wake flag. The entire volatile state of

the device is reset.

Idle

0x02

The ATSHA204A goes into the idle state and ignores all subsequent I/O

transitions until the next Wake flag. The contents of TempKey and RNG Seed

registers are retained.

Command

0x03

Write subsequent bytes to sequential addresses in the input command buffer

that follow previous writes. This is the normal operation.

Reserved

0x04 - 0xFF These addresses should not be sent to the device.

6.2.2

Command Completion Polling

After a complete command has been sent to the ATSHA204A, the device will be busy until the command

computation completes. The system has two options for this delay:

•

Polling

The system should wait tEXEC (typical) and then send a read sequence (See Section I2C

Transmission from the ATSHA204A Device). If the device NACKs the device address, then it is

still busy. The system may delay for some time or immediately send another read sequence, again

looping on NACK. After a total delay of tEXEC (max), the device will have completed the

computation and can return the results.

•

Single Delay

The system should wait tEXEC (max), after which the device will have completed execution and the

result can be read from the device using a normal read sequence.

ATSHA204A

I2C Interface

DS40002025A-page 31

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