HCS200

DS40138A-page 4

Preliminary

© 1996 Microchip Technology Inc.

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.

FIGURE 2-1:

TYPICAL CIRCUITS

TABLE 2-1:

PIN DESCRIPTIONS

Note:

loads, a resistor with a minimum value of 50

Ω

clamping of PWM at 9.0V in the event of PWM

overshoot.

Name

Pin

Number

Description

S0

1

Switch input 0

S1

2

Switch input 1

S2

3

Switch input 2/Clock pin when in

programming mode

5

Ground reference connection

PWM

6

Pulse width modulation (PWM)

output pin/Data pin for program-

ming mode

8

Positive supply voltage connec-

tion

B0

Tx out

S0

S1

S2

PWM

Vss

2 button remote control

B1

Tx out

S0

S1

S2

PWM

Vss

4 button remote control (Note)

B3 B2 B1 B0

+12V

(Note 2) R

+12V

NC

NC

NC

NC

(Note 2) R

Note 1:

Up to 7 functions can be implemented by pressing

more than one button simultaneously or by using a

suitable diode array.

The high security level of the HCS200 is based on the pat-

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, fixed 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. Overflow 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 pre

ssed, a reset will immediately be forced and the

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

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

Reset and Debounce Delay

(10 ms)

Sample Inputs

Update Sync Info

Encrypt With

Load Transmit Register

Buttons

Added

?

All

Buttons

Released

?

(A button has been pressed)

Transmit

Stop

No

Yes

No

Yes

Encryption Key

Complete Code

Word Transmission