ATSHA204 ATMEL [ATMEL Corporation], ATSHA204 Datasheet - Page 19

• Manufacturer Part Number: ATSHA204
• Description: Atmel CryptoAuthentication
• Manufacturer: ATMEL [ATMEL Corporation]

5.1
5.2
5.2.1.1 Transmit Flag
I/O Tokens
There are a number of I/O tokens that may be transmitted over the single-wire interface:
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.
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.
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.
Value
0x77
0x88
0xBB
0xCC
Input:
Output: (from the Atmel ATSHA204)
Name
Command
Transmit
Idle
Sleep
(to the Atmel ATSHA204)
Wake
Zero
One
ZeroOut
OneOut
I/O flags
Meaning
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.
This command tells the device to wait for a bus turnaround time and then start transmitting its
response to the previously transmitted command block.
Upon receipt of an idle flag, the device goes into the idle mode and remains there until the next
wake token is received.
Upon receipt of a sleep flag, the device enters the low-power sleep mode until the next Wake token
is received.
Wake the device up from either sleep or idle states.
Send a single bit from the system to the device with a value of zero.
Send a single bit from the system to the device with a value of one.
Send a single bit from the device to the system with a value of zero.
Send a single bit from the device to the system with a value of one.
All other values are reserved and should not be used
Atmel ATSHA204 [DATASHEET]
8740D−CRYPTO−3/12
19