HCS412 datasheet(21/44 Pages) MICROCHIP

21 / 44 page

Preliminary

DS41099C-page 21

HCS412

4.3.1

ANTICOLLISION

Multiple tokens in the same inductive field will simulta-

neously

respond

inductive

commands.

The

responses will collide making token authentication

impossible. Enabling anticollision allows addressing of

an individual token, regardless how many tokens are in

the field.

The HCS412 method is that all tokens trained to a

given vehicle will have the same 25 MSb’s of their serial

number. The serial numbers of up to 8 tokens trained to

access a given vehicle will differ only in the 3 LSb’s.

Think of the 25 MSb’s of the HCS412's serial number

as the vehicle ID and the 3 LSb’s as the token ID. The

vehicle ID associates the token with a given vehicle

and the token ID makes it a uniquely addressable

(selectable) 1 of 8 possible tokens authorized to access

the vehicle.

The transponder reader addresses an individual token,

HCS412, by sending a ‘SELECT ENCODER’ command.

The command is followed by from 1 to 25 bits of the

HCS412's serial number, starting with bit 3 (Least Sig-

nificant bit first) (Figure 4-3).

Clocking out ‘1’s then increments the 3 LSb’s, the first

‘1’ setting the bits to 000b. When the value matches

the 3 LSb’s of a token, the token responds with an

Encoder Select Acknowledge. The reader must halt

clocking out further ‘1’s or risk selecting multiple

tokens. Any remaining tokens in the field will be unse-

lected, responding only if a new device selection

sequence selects them. Removing the field will also

RESET a selected/unselected state if removed long

enough to result in a device RESET.

The ability to isolate a single HCS412 for communica-

tion greatly depends on the number of Most Significant

serial number bits included in the device selection

sequence. The more serial number bits sent, the more

narrow the device selection. All bits not transmitted are

treated as wildcards. Sending only 1 bit, bit 3 as a ‘0’,

will only narrow the number of tokens allowed to

respond to all with bit 3 equal to ‘0’. When the transpon-

der reader sends the full 25 MSb’s of the serial number,

it narrows all possible tokens down to only those

trained to the vehicle - only those tokens whose serial

number’s 25 MSb’s match.

TABLE 4-3:

DEVICE SELECT COMMAND

FIGURE 4-3:

ANTICOLLISION - DEVICE SELECTION

Command

Description

Expected data In

Response

00000

Select HCS412, used if Anticolli-

sion enabled

The desired HCS412’s serial

number

Encoder select Acknowledge if

serial number match

1 to 25 bits of the

Serial Number,

Encoder

Select

ACK

Inductive

Comms

TESA

Command

TOTD

Start

2 LFTE

Activate

Field

ACK

Delay to

Command

Delay to

Serial

Most Sig X Bits

3 LSb’s

Clock Serial

of Serial Number

Delay

ACK

28-bit Serial Number

1 to 25 bits of the

Serial Number,

starting with Bit 3.

Communication from reader to HCS412

Communication from HCS412 to reader

2ms

000b

010b

001b

011b

4th ‘1’ interrupted

by ACK, indicating

selection @ LSb = 011b

Send ‘1’s to

increment 3LSb’s

Start

2 LFTE

Start

2 LFTE

starting with Bit 3.

HCS412 数据表(PDF) 21 Page - Microchip Technology

HCS412 数据表(HTML) 21 Page - Microchip Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44

数据表下载

链接网址

HCS412 数据表(PDF) 21 Page - Microchip Technology

HCS412 数据表(HTML) 21 Page - Microchip Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44

数据表 下载

链接网址

数据表下载