HCS410 Datasheet, PDF (14/36 Pages) Microchip Technology – KEELOQ CODE HOPPING ENCODER AND TRANSPONDER

HCS410
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.
Note: When IFF2 is enabled, seed transmissions
will not be allowed.
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
PPM Decoder Commands
Start or
previous
bit
0
3 TE
1 TE
PPM Encoder Response
0
TE TE
1
5 TE
1 TE
FIGURE 2-16: OVERVIEW OF IFF OPERATION
IFF
Activate Opcode
32/16-bit Challenge
Activate
Opcode
WRITE
16 bit Data
Activate
Opcode
READ
16 bit Data
1
2 TE TE
32/16-bit IFF Response
OK
Opcode
Opcode
Opcode
DS40158C-page 14
Preliminary
© 1997 Microchip Technology Inc.