ATSHA204 ATMEL [ATMEL Corporation], ATSHA204 Datasheet - Page 18

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

4.2
5.
Sharing the Interface
Multiple CryptoAuthentication devices may share the same interface, as follows:
Steps a and b are repeated for each device on the wire. If the system has completed communications with the final device, it
should wake all the devices up and then put all the devices to sleep to reduce total power consumption.
The device uses the selector byte within the configuration zone to determine which device stays awake – only that device with
a selector value that matches the input parameter of the Pause command stays awake. In order to facilitate late configuration
of systems that use the multi-device sharing mode, the following three update capabilities for the selector byte are supported:
Single-wire Interface
In this mode, communications to and from the ATSHA204 take place over SDA, a single, asynchronously timed wire, and the
SCL pin is ignored.
Note:
The overall communications structure is a hierarchy:
See the Atmel website for the appropriate application notes for more details on how to use any microprocessor to easily
generate the signaling necessary to send these elements to the device, including C source code libraries. Also, see Section
10.2, “Wiring Configuration for Single-wire Interface,” for more information about how to connect the device in the single-wire
interface mode.
a.
b.
1.
2.
3.
Tokens
Flags
Blocks
Packets
System issues a Wake token (see Section 5.1) to wake up all devices.
The system issues the Pause command to put all but one of the devices into idle mode. Only the remaining device then
sees any commands the system sends. When the system has completed talking to the one active device, it sends an
idle flag, which the idle devices ignore but which puts the single remaining active device into the idle mode. See Section
8.10, “Pause Command,” for more details.
Unlimited Updates
One-time Field Update
Fixed Selector Value
At any time, the UpdateExtra command can be executed to write the value in the selector field of the configuration
zone. To enable this mode, set the SelectorMode byte in the configuration zone to zero.
If the SelectorMode byte is set to a non-zero value and the selector byte is set to a zero value prior to locking the
configuration zone, then at any time after the configuration zone is locked the UpdateExtra command can be used
one time to set Selector to a non-zero value. The UpdateExtra command is not affected by the LockValue byte.
The selector byte can never be modified after the configuration zone is locked if both SelectorMode and Selector are
set to non-zero values. The UpdateExtra command will always return an error code.
The sleep current specification values are guaranteed only if the SCL pin is held low or left unconnected.
I/O tokens implement a single data bit transmitted on the bus, or the wake-up event.
Flags consist of eight tokens (bits) that convey the direction and meaning of the next group of bits (if any)
that may be transmitted.
Blocks of data follow the command and transmit flags. They incorporate both a byte count and a checksum
to ensure proper data transmission.
Packets of bytes form the core of the block (minus the byte count and CRC). They are either the input or
output parameters of a CryptoAuthentication command or status information from the Atmel ATSHA204.
Atmel ATSHA204 [DATASHEET]
8740D−CRYPTO−3/12
18