ATSHA204 datasheet(19/65 Pages) ATMEL

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Atmel ATSHA204 [DATASHEET]

8740D

−CRYPTO−3/12

5.1

I/O Tokens

There are a number of I/O tokens that may be transmitted over the single-wire interface:

Input:

(to the Atmel ATSHA204)

Wake

Wake the device up from either sleep or idle states.

Zero

Send a single bit from the system to the device with a value of zero.

One

Send a single bit from the system to the device with a value of one.

Output: (from the Atmel ATSHA204)

ZeroOut

Send a single bit from the device to the system with a value of zero.

OneOut

Send a single bit from the device to the system with a value of one.

The waveforms are the same in either direction. There are some differences in timing, however, based on the expectation that

the host has a very accurate and consistent clock, while the ATSHA204 has significant part-to-part variability in its internal

clock generator, due to normal manufacturing and environmental fluctuations.

The bit timings are designed to permit a standard UART running at 230.4K baud to transmit and receive the tokens efficiently.

Each byte transmitted or received by the UART corresponds to a single bit received or transmitted by the device.

The Wake token is special in that it requires an extra long low pulse on the SDA pin, which cannot be confused with the

shorter low pulses that occur during a data token (Zero, One, ZeroOut, OneOut). Devices that are in either the idle or sleep

state ignore all data tokens until they receive a legal Wake token. Do not send a Wake token to devices that are awake, as

they will lose synchronization because the waveform can be resolved to neither a legal one nor zero. See Section 5.3.2 for the

procedure to regain synchronization.

5.2

I/O Flags

The system is always the bus master, so before any I/O transaction, the system must send an 8-bit flag to the device to

indicate the I/O operation to be subsequently performed, as shown in Table 5-1.

Table 5-1.

I/O flags

Value

Name

Meaning

0x77

Command

After this flag, the system starts sending a command block to the device.

The first bit of the block can follow immediately after the last bit of the flag.

0x88

Transmit

This command tells the device to wait for a bus turnaround time and then start transmitting its

response to the previously transmitted command block.

0xBB

Idle

Upon receipt of an idle flag, the device goes into the idle mode and remains there until the next

wake token is received.

0xCC

Sleep

Upon receipt of a sleep flag, the device enters the low-power sleep mode until the next Wake token

is received.

All other values are reserved and should not be used

5.2.1.1 Transmit Flag

The transmit flag is used to turn the bus around so that the ATSHA204 can send data back to the system. The bytes that the

device returns to the system depend on the current state of the device, and may include either status, error code, or command

results.

When the device is busy executing a command, it ignores the SDA pin and any flags sent by the system. See Table 8-4 for

execution delays in the device for each command type. The system must observe these delays after sending a command to

the device.

ATSHA204 Datasheet(PDF) 19 Page - ATMEL Corporation

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