HCS410 datasheet(13/46 Pages) MICROCHIP

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HCS410

DS40158F-page 13

2.4

IFF Mode

IFF mode allows the decoder to perform an IFF valida-

tion, to write to the user EEPROM and to read from the

user EEPROM. Each operation consists of the decoder

sending an opcode data and the HCS410 giving a

response.

There are two IFF modes: IFF1 and IFF2. IFF1 allows

only one key IFF, while IFF2 allows two keys to be

used.

It is possible to use the HCS410 as an IFF token with-

out using a magnetic field for coupling. The HCS410

can be directly connected to the data line of the

decoder as shown in Figure 2-3. The HCS410 gets its

power from the data line as it would in normal transpon-

der mode. The communication is identical to the com-

munication used in transponder mode.

2.4.1

IFF MODE ACTIVATION

The HCS410 will enter IFF mode if the capacitor/induc-

tor resonant circuit generates a voltage greater than

approximately 1.0 volts on LC0. After the verified appli-

cation of power and elapse of the normal reset period,

the device will start responding by pulsing the DATA

line (LC0/1) with pulses as shown in Figure 2-17. This

action will continue until the pulse train is terminated by

receiving a start signal of duration 2TE, on the LC inputs

before the next expected marker pulse. The device

now enters the IFF mode and expects to receive an

‘Opcode’ and a 0/16/32-bit Data-stream to react on.

The data rate (TE) is determined by the TBSL bits in the

configuration word. See Section 3.0 for additional

details.

2.4.2

IFF DECODER COMMANDS

As shown in Figure 2-15, a logic 1 and 0 are differenti-

ated by the time between two rising edges. A long

pulse indicates a 1; a short pulse, a 0.

FIGURE 2-15: MODULATION FOR IFF COMMUNICATION

FIGURE 2-16: OVERVIEW OF IFF OPERATION

Note:

When IFF2 is enabled, seed transmissions

will not be allowed.

3 TE

5 TE

2 TE

Start or

bit

PPM Decoder Commands

PPM Encoder Response

Activate

Opcode

32/16-bit Challenge

32/16-bit IFF Response

Opcode

Activate

Opcode

16-bit Data

Opcode

Activate

Opcode

16-bit Data

IFF

WRITE

READ

Opcode

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