ST25DV04K datasheet(77/200 Pages) STMICROELECTRONICS

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7.4.3

Modes

The term “mode” refers to the mechanism used in a request to specify the set of ST25DVxxx devices that shall

execute the request.

Addressed mode

When the Address_flag is set to 1 (Addressed mode), the request contains the Unique ID (UID) of the addressed

ST25DVxxx.

Any ST25DVxxx that receives a request with the Address_flag set to 1 compares the received Unique ID to its

own. If it matches, then the ST25DVxxx executes the request (if possible) and returns a response to the VCD as

specified in the command description.

If the UID does not match, then it remains silent.

Non-addressed mode (general request)

When the Address_flag is cleared to 0 (Non-Addressed mode), the request does not contain a Unique ID.

Select mode

When the Select_flag is set to 1 (Select mode), the request does not contain a unique ID. The ST25DVxxx in the

Selected state that receives a request with the Select_flag set to 1 executes it and returns a response to the VCD

as specified in the command description.

Only the ST25DVxxx in the Selected state answers a request where the Select_flag is set to 1.

The system design ensures that only one ST25DVxxx can be in the Select state at a time.

7.4.4

Request format

The request consists of:

•

an SOF,

•

flags,

•

a command code,

•

parameters and data,

•

a CRC,

•

an EOF.

Table 93. General request format

SOF

Request_flags

Command code

Parameters

Data

2 byte CRC

EOF

7.4.5

Request flags

In a request, the “flags” field specifies the actions to be performed by the ST25DVxxx and whether corresponding

fields are present or not.

The flags field consists of eight bits. Bit 3 (Inventory_flag) of the request flag defines the contents of the four

MSBs (bits 5 to 8). When bit 3 is reset (0), bits 5 to 8 define the ST25DVxxx selection criteria. When bit 3 is set

(1), bits 5 to 8 define the ST25DVxxx Inventory parameters.

ST25DV04K ST25DV16K ST25DV64K

RF protocol description

DS10925 - Rev 9

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