ATSHA204A datasheet(32/93 Pages) MICROCHIP

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6.3

I2C Transmission from the ATSHA204A Device

When the ATSHA204A is awake and not busy, the bus master can retrieve the current buffer contents

from the device using an I2C read. If valid command results are available, the size of the block returned is

determined by the particular command that has been run (See Section Security Commands); otherwise,

the size of the block (and the first byte returned) is always four: count, status/error and 2-byte CRC. The

bus timing is shown in Figure I2C Synchronous Data Timing.

Table 6-3. I2C transmission from ATSHA204A

Name

I2C Name

Direction Description

Device

Address

Device

Address

To Slave

This byte selects a particular device on the I2C interface and the

ATSHA204A is selected if bits 1 through 7 of this byte match bits 1 through 7

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

standard I2C R/W pin and should be one to indicate that the bytes following

the device address travel from the slave to the master (read).

Data

Data1,N

To Master

The output block, consisting of the count and status/error byte or the output

packet followed by the 2-byte CRC per Section 8.2.

The status, error, or command outputs can be read repeatedly by the master. Each time a Read

command is sent to the ATSHA204A along the I2C interface, the device transmits the next sequential byte

in the output buffer. See the following section for details on how the device handles the address counter.

If the ATSHA204A is busy, idle, or asleep, it will NACK the device address on a read sequence. If a partial

command has been sent to the device, then it will NACK the device address, but float the bus during the

data intervals.

6.4

Address Counter

Writes to and/or reads from the ATSHA204A I/O buffer over the I2C interface are treated as if the device

were a FIFO. Either the I2C byte or block write/read protocols can be used. The number of bytes

transferred with each block sequence does not affect the operation of the device.

The first byte transmitted to the device is treated as the count byte. Any attempt to send more than this

number of bytes or any attempts to write beyond the end of the I/O buffer (84 bytes) causes the

ATSHA204A to NACK those bytes.

After the Host writes a single command byte to the input buffer, device Read commands from the Host

are prohibited until after the device completes command execution. Attempts to read from the device prior

to the last command byte being sent results in an ACK of the device address but all ones (0xFF) on the

bus. If the master attempts to send a read byte to the device during command execution, the device will

NACK the device address.

Data may be read from the device under the following three conditions:

•

Upon power-up, the single byte, 0x11 (See Section Command Opcodes, Short Descriptions

and Execution Times), can be read inside a four byte block.

•

If a complete block has been received by the device, but there are any errors in parsing or

executing the command, a single byte of error code is available, also inside a four byte block.

•

Upon completion of command execution, from 1 to 32 bytes of command result are available to be

read inside a block of 4 to 35 bytes.

ATSHA204A

I2C Interface

DS40002025A-page 32

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