HCS301 Datasheet, PDF(4/20 Page) Microchip Technology

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HCS301 Datasheet, PDF (4/20 Pages) Microchip Technology – KEELOQ CODE HOPPING ENCODER

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HCS301

2.0 DEVICE OPERATION

As shown in the typical application circuits (Figure 2-1),

the HCS301 is a simple device to use. It requires only

the addition of buttons and RF circuitry for use as the

transmitter in your security application. A description of

each pin is described in Table 2-1.

Note:

When VDD > 9.0V and driving low capacitive

loads, a resistor with a minimum value of 50â¦

should be used in line with VDD. This prevents

clamping of PWM at 9.0V in the event of PWM

overshoot.

FIGURE 2-1: TYPICAL CIRCUITS

+12V

(Note 2) R

VDD

LED

PWM

Tx out

VSS

2 button remote control

B4 B3 B2 B1 B0

(Note 2) R

VDD

+12V

VDD

LED

PWM

VSS

Tx out

5 button remote control (Note1)

Note 1:

Up to 15 functions can be implemented by pressing

more than one button simultaneously or by using a

suitable diode array.

2: Resistor (R) is recommended for current limiting.

TABLE 2-1: PIN DESCRIPTIONS

Name

Number

Description

VSS

PWM

LED

VDD

1 Switch input 0

2 Switch input 1

3 Switch input 2/Can also be clock

pin when in programming mode

4 Switch input 3/Clock pin when in

programming mode

5 Ground reference connection

6 Pulse width modulation (PWM)

output pin/Data pin for

programming mode

7 Cathode connection for directly

driving LED during transmission

8 Positive supply voltage

connection

The high security level of the HCS301 is based on the pat-

ented KEELOQ technology. A block cipher based on a block

length of 32 bits and a key length of 64 bits is used. The

algorithm obscures the information in such a way that even

if the transmission information (before coding) differs by

only 1 bit from the information in the previous transmis-

sion, the next coded transmission will be totally different.

Statistically, if only 1 bit in the 32-bit string of information

changes, approximately 50 percent of the coded transmis-

sion will change. The HCS301 will wake up upon detecting

a switch closure and then delay approximately 10 ms for

switch debounce (Figure 2-2). The synchronization infor-

mation, ï¬xed information, and switch information will be

encrypted to form the hopping code. The encrypted or

hopping code portion of the transmission will change every

time, even if the same button is pushed again. A code that

has been transmitted will not occur again for more than

64K transmissions. This will provide more than 18 years of

typical use before a code is repeated, based on 10 opera-

tions per day. Overï¬ow information sent from the encoder

can be used by the decoder to extend the number of

unique transmissions to more than 192K.

If, in the transmit process, it is detected that a new but-

ton(s) has been pressed, a reset will immediately be

forced and the code word will not be completed. Please

note that buttons removed will not have any effect on the

code word unless no buttons remain pressed. In this case,

the code word will be completed and the power down will

occur.

FIGURE 2-2: ENCODER OPERATION

Power Up

(A button has been pressed)

Reset and Debounce Delay

(10 ms)

Sample Inputs

Update Sync Info

Encrypt With

Encryption Key

Load Transmit Register

Transmit

Yes

Buttons

Added?

All

Buttons

Released?

Yes

Complete Code

Word Transmission

Stop

DS21143A-page 4

Preliminary

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