XRA00 datasheet(24/40 Pages) STMICROELECTRONICS

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XRA00

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BASIC COMMANDS - OVERVIEW

The XRA00 provides six Basic commands, de-

scribed in the following paragraphs.

ScrollID

The ScrollID command is a Basic command that

gives rise to a response from the XRA00.

When the ScrollID command is issued, the XRA00

responds if the data sent by the Reader in the

[VALUE] field matches the XRA00's internal mem-

ory starting at the location specified by the [PTR]

field. Data in the [VALUE] field is compared to the

XRA00 memory, from the lowest to the highest ad-

dress. Only XRA00 devices that match all of the

bits in the [VALUE] field reply to the Reader.

XRA00 devices that fail the match or fail a parity

test on any of the parity bits do not modulate.

The XRA00 devices that match the data sent by

the Reader reply by sending back an 8-bit pream-

ble, a 16-bit CRC for error checking followed by

the entire 96-bit ePC code.

■

Any unlocked XRA00 seeing the command

will reply by sending back an 8-bit preamble,

16-bit CRC and its entire 96-bit ePC code,

plus the Kill code and Lock code location bits.

■

Any locked XRA00 seeing the command will

reply by sending back an 8-bit preamble, 16-

bit CRC and its entire 96-bit ePC code.

Data sent by the Reader to the XRA00 may be of

variable length. ScrollID can be used to look for

specific XRA00 devices or test for the presence of

specific groups of XRA00 devices in the field. Data

sent by the XRA00 has a fixed length.

Example of a ScrollID Command . A Reader is-

sues a command containing the following data:

[CMD] =

00000001b

(ScrollID)

[PTR] =

00000111b

(0x07)

[LEN] =

00001001b

(0x09)

[VALUE] = 000101101b

(0x2D)

XRA00 devices will attempt to check 9 bits of their

address data, starting at bit 7, against the data

specified in the [VALUE] field. XRA00 devices

whose data matches respond with a ScrollID Re-

ply.

Table 8. shows the case of three XRA00 devices.

XRA00 1 and XRA00 3 respond to the command

but XRA00 2 does not. Underlined bits in XRA00

memory are compared with the [VALUE] data.

Here, bits 7 through 15 are compared.

The XRA00 devices start by modulating the lowest

memory address data bit onward up to the highest

memory address data bit. This means that in Table

8., modulation is from right to left.

Table 8. Example of a ScrollID Operation

XRA00 ID Code/Bit Number

XRA00 responds to ScrollID command

Towards Highest

Address Bit

Lowest Address Bit

Bit Number

...321098765432109876543210

XRA00 1 ID

...010001000001011011101010b

YES

XRA00 2 ID

...100111100001001010010010b

NO (bit 10 fails to match)

XRA00 3 ID

...101101010001011011110111b

YES

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