HCS412 datasheet(18/44 Pages) MICROCHIP

18 / 44 page

HCS412

DS41099C-page 18

Preliminary

4.0

TRANSPONDER OPERATION

4.1

IFF Mode

The HCS412’s IFF Mode allows it to function as a bi-

directional token or transponder. IFF mode capabilities

include the following.

• A bi-directional challenge and response sequence

for IFF validation. HCS412 IFF responses may be

directed to use one of two available encryption

algorithms and one of two available crypt keys.

• Read selected EEPROM areas.

• Write selected EEPROM areas.

• Request a code hopping transmission.

• Proximity Activation of a code hopping transmis-

sion.

4.2

IFF Communication

The transponder reader initiates each communication

by turning on the low frequency field, then waits for a

HCS412 to Acknowledge the field.

The HCS412 enters IFF mode upon detecting a signal

on the LC0 LF antenna input pin. Once the incoming

signal has remained high for at least the power-up time

TPU, the device responds with a field Acknowledge

sequence indicating that the it has detected the LF

field, is in IFF Mode and is ready to receive commands

(Figure 4-1). The HCS412 will repeat the field Acknowl-

edge sequence every 255 LFTE‘s if the field remains

but no command is received (Figure 4-1).

The transponder reader follows the HCS412’s field

Acknowledge by sending the desired 5-bit command

and associated data. LF commands are always pre-

ceded by a 2 LFTE low START pulse and are Pulse

Position Modulated (PPM) as shown in Figure 4-2. The

last command or data bit should be followed by leaving

the field on for a minimum of 6 LFTE.

HCS412 PPM data responses are preceded by a 1

LFTE low pulse, followed by a 01b preamble before the

data begins (Figure 4-4). The responses are sent either

on the LC antenna output alone or on both the LC out-

put and the DATA pin, depending on the device config-

uration (Section 4.4.2). This allows for short-range LF

responses as well as long-range RF responses.

Data to and from the HCS412 is always sent Least Sig-

nificant bit first. The data length and modulation format

vary according to the command and the transmission

path.

Data Length and Commands:

• Read and Write transfers 16 bits of data.

• Challenge and Response transfers 32 bits of data.

Modulation Format and Transmission Path:

• LF responses on the LC output are Pulse Position

Modulated (PPM) according to Figure 4-2.

• RF responses on the DATA pin modulate accord-

ing to standard encoder transmissions

(Figure 3-5, Figure 3-6).

Communication with the HCS412 over the low fre-

quency path (LC pins) uses a basic Timing Element,

LFTE. The Low Frequency Baud Rate Select option,

LFBSL, sets LFTE to either 100

µs or 200 µs

(Table 4-1).

The response on the DATA pin uses the Encoder

mode’s RF Timing Element (RFTE) and the modulation

format set by the MOD configuration option (Table 3-6).

The RF responses use the standard Encoder mode for-

mat with the 32-bit hopping portion replaced by the

response data (Figure 4-19). If the response is only 16

bits, the 32 bits will contain 2 copies of the response

(Figure 4-16).

TABLE 4-1:

LOW FREQUENCY BAUD

RATE SELECT BITS

4.2.1

CALCULATING COMMUNICATION TE

The HCS412’s internal oscillator will vary ±10% over

the device’s rated voltage and temperature range.

When the oscillator varies, both its transmitted TE and

expected TE when receiving will vary.

Communication reliability with the token may be

improved by calculating the HCS412’s TE from the field

Acknowledge sequence and using this measured time

element in communication to and in reception routines

from the token.

Always begin and end the time measurement on rising

edges. Whether LF or RF, the falling edge decay rates

may vary but the rising edge relationships should

remain consistent. A common TE calculation method

would be to time an 8 TE sequence, then divide the

value down to determine the single TE value. An 8 TE

measurement will give good resolution and may be

easily right-shifted (divide by 2) three times for the math

portion of the calculation (Figure 4-1).

Accurately measuring TE is important for communicat-

ing to an HCS412 as well as for inductive programming

a device. The configuration word sent during program-

ming contains the 4-bit oscillator tuning value. Accu-

rately determining TE allows the programmer to

calculate the correct oscillator tuning bits to place in the

configuration word, whether the device oscillator needs

to be sped up or slowed down to meet its desired TE.

LFBSL

LFTE

200

µs

100

µs

HCS412 数据表(PDF) 18 Page - Microchip Technology

HCS412 数据表(HTML) 18 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