HCS412 datasheet(27/44 Pages) MICROCHIP

27 / 44 page

Preliminary

DS41099C-page 27

HCS412

4.3.8

ENABLE DEFAULT IFF COMMUNICATION

The ENABLE DEFAULT IFF COMMUNICATION com-

mand defaults certain HCS412 communication options

such that the transponder reader may communicate to

the device with a common (safe) protocol. The default

setting remains for the duration of the communication,

returning to normal only after a device RESET.

Default IFF communication settings:

• Anticollision disabled

• RF echo disabled

•200

µs LF baud rate.

TABLE 4-9:

DEFAULT IFF COMMUNICATION COMMANDS

FIGURE 4-14: ENABLE DEFAULT IFF COMMUNICATION

4.4

IFF Communication Special Features

TABLE 4-10:

LF COMMUNICATION

SPECIAL FEATURES (LFSP)

4.4.1

PASSIVE PROXIMITY ACTIVATION

(LFSP = 10)

Enabling the Proximity Activation configuration option

allows the HCS412 to transmit a hopping code trans-

mission in response to a signal present on the LC0 pin.

The HCS412 sends out Field Acknowledge Sequence

in response to detecting the LF field (Figure 4-1). If the

HCS412 does not receive a command before the sec-

ond field Acknowledge sequence [within 255 LFTE‘s], it

will transmit a normal code hopping transmission for 2

seconds on the DATA pin. After 2 seconds the HCS412

reverts to normal transponder mode.

The 2 second transmission does not repeat when the

device is in the presence of a continuous LF field. The

HCS412 must be RESET, remove and reapply the LF

field, to activate another transmission.

The button status used in the code hopping transmis-

sion indicates a proximity activation by clearing the S0,

S1 and S2 button activation flags.

FIGURE 4-15: PROXIMITY ACTIVATION

Command

Description

Expected data In

Response

11100

Enable default IFF communication

None

Communication from reader to HCS412

Communication from HCS412 to reader

ACK

pulses

Inductive Comms

RF Comms

TATO

Activate

Field

ACK

Delay to

Command

Delay

Next Command

Command

Start

2 LFTE

LFSP1:0

Description

No special options enabled

Anticollision enabled (Section 4.3.1)

Proximity Activation enabled

Anticollision and RF Echo enabled

DATA (RF)

ACK

LF Communication from reader to HCS412

LF Communication from HCS412 to reader

Inductive

(LF)

No command received from

reader for 255 LFTE.

Transmit hopping code for 2

seconds

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