RFHCS362G_11 Datasheet, PDF (2/54 Pages) Microchip Technology – KEELOQ® Code Hopping Encoder with UHF ASK/FSK Transmitter

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.
DS41189B-page 2
© 2011 Microchip Technology Inc.