HCS200 Datasheet, PDF(4/16 Page) Microchip Technology

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HCS200 Datasheet, PDF (4/16 Pages) Microchip Technology – KEELOQ CODE HOPPING ENCODER

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HCS200

2.0 DEVICE OPERATION

As shown in Figure 2-1, the HCS200 is a simple device

to use. It requires only the addition of buttons and RF

circuitry for use as the transmitter in your security appli-

cation. 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

(Note 2) R

+12V

VDD

PWM

Tx out

Vss

2 button remote control

(Note 2) R

B3 B2 B1 B0

+12V

VDD

S2 PWM

Vss

Tx out

4 button remote control (Note)

Note 1:

Up to 7 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

VDD

1 Switch input 0

2 Switch input 1

3 Switch input 2/Clock pin when in

programming mode

5 Ground reference connection

6 Pulse width modulation (PWM)

output pin/Data pin for program-

ming mode

8 Positive supply voltage connec-

tion

The high security level of the HCS200 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 algo-

rithm obscures the information in such a way that even if the

transmission information (before coding) differs by only one bit

from the information in the previous transmission, the next

coded transmission will be totally different. Statistically, if only

one bit in the 32-bit string of information changes, approxi-

mately 50 percent of the coded transmission will change. The

HCS200 will wake up upon detecting a switch closure and

then delay approximately 10 ms for switch debounce

(Figure 2-2). The synchronization information, ï¬xed informa-

tion, and switch information will be encrypted to form the hop-

ping 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 operations 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 button(s) has

been pressed, a reset will immediately be forced and the

code word will not be completed. Please note that but-

tons removed will not have any effect on the code word

unless no buttons remain pressed in which 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

DS40138A-page 4

Preliminary

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