RFHCS362G datasheet(3/60 Pages) MICROCHIP

3 / 60 page

Preliminary

DS41189A-page 3

rfHCS362G/362F

1.0

GENERAL DESCRIPTION

The rfHCS362G/362F is a code hopping encoder plus

UHF transmitter designed for secure wireless com-

mand and control systems. The rfHCS362G/362F uti-

lizes the KEELOQ® code hopping technology which

incorporates high security in a small package outline at

a low cost to make this device well suited for unidirec-

tional remote keyless entry systems and access control

systems.

The rfHCS362G/362F combines a 32-bit hopping code

generated by a nonlinear encryption algorithm with a

28/32-bit serial number and 9/5 status bits to create a

69-bit transmission stream. The length of the transmis-

sion strongly resists the threat of code scanning. The

code hopping mechanism makes each transmission

unique, thus rendering code capture and resend (code

grabbing) schemes virtually useless.

The encryption key, serial number and configuration

data are stored in an EEPROM array which is not

accessible via any external connection. The EEPROM

data is programmable but read protected. The data can

be verified only after an automatic erase and program-

ming operation. This protects against attempts to gain

access to keys or manipulate synchronization values.

The rfHCS362G/362F provides an easy to use serial

interface for programming the necessary keys, system

parameters and configuration data.

The transmitter is a fully integrated UHF ASK/FSK

transmitter consisting of crystal oscillator, Phase-

Locked Loop (PLL), open-collector differential-output

Power Amplifier (PA), and mode control logic. External

components consist of bypass capacitors, crystal, and

PLL loop filter. There are no internal electrical connec-

tions between the encoder and the transmitter. The

encoder oscillator is independent from the transmitter

crystal oscillator.

The rfHCS362G is capable of Amplitude Shift Keying

(ASK) modulation by turning the PA on and off. The

rfHCS362F is capable of ASK or Frequency Shift Key-

ing (FSK) modulation by employing an internal FSK

switch to pull the transmitter crystal via a second load

capacitor.

The rfHCS362G/362F is a single channel device. The

transmit frequency is fixed and set by an external refer-

ence crystal. Transmit frequencies in the range of 310

to 440 MHz can be selected. Output drive is an open-

collector differential amplifier. The differential output is

well suited for loop antennas. Output power is adjust-

able from +2 dBm to -12 dBm in six discrete steps.

The rfHCS362G/362F are radio frequency (RF) emit-

ting devices. Wireless RF devices are governed by a

country’s regulating agency. For example, in the United

States it is the Federal Communications Committee

(FCC) and in Europe it is the European Conference of

Postal

and

Telecommunications

Administrations

(CEPT). It is the responsibility of the designer to ensure

that their end product conforms to rules and regulations

of the country of use and/or sale.

RF devices require correct board level implementation

in order to meet regulatory requirements. Layout con-

siderations are given in Section 6.0 UHF ASK/FSK

Transmitter.

1.1

Important Terms

The following is a list of key terms used throughout this

data sheet. For additional information on KEELOQ and

Code Hopping refer to Technical Brief 3 (TB003).

• RKE - Remote Keyless Entry

• Button Status - Indicates what button input(s)

activated the transmission. Encompasses the 4

button status bits S3, S2, S1 and S0 (Figure 3-6).

• Code Hopping - A method by which a code,

viewed externally to the system, appears to

change unpredictably each time it is transmitted.

• Code word - A block of data that is repeatedly

transmitted upon button activation (Figure 3-6).

• Transmission - A data stream consisting of

repeating code words (Figure 10-1).

• Encryption key - A unique and secret 64-bit

number used to encrypt and decrypt data. In a

symmetrical block cipher such as the KEELOQ

algorithm, the encryption and decryption keys are

equal and will be referred to generally as the

encryption key.

• Encoder - A device that generates and encodes

data.

• Encryption Algorithm - A recipe whereby data is

scrambled using a encryption key. The data can

only be interpreted by the respective decryption

algorithm using the same encryption key.

• Decoder - A device that decodes data received

from an encoder.

• Decryption algorithm - A recipe whereby data

scrambled by an encryption algorithm can be

unscrambled using the same encryption key.

• Learn – Learning involves the receiver calculating

the transmitter’s appropriate encryption key,

decrypting the received hopping code and storing

the serial number, synchronization counter value

and encryption key in EEPROM. The KEELOQ

product family facilitates several learning strate-

gies to be implemented on the decoder. The fol-

lowing are examples of what can be done.

- Simple Learning

The receiver uses a fixed encryption key,

common to all components of all systems by

the same manufacturer, to decrypt the

received code word’s encrypted portion.

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