HCS301

DS21143A-page 4

Preliminary

© 1996 Microchip Technology Inc.

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.

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/Can also be clock

pin when in programming mode

S3

4

Switch input 3/Clock pin when in

programming mode

5

Ground reference connection

PWM

6

Pulse width modulation (PWM)

output pin/Data pin for

programming mode

LED

7

Cathode connection for directly

driving LED during transmission

8

Positive supply voltage

connection

B0

Tx out

S0

S1

S2

S3

LED

PWM

2 button remote control

B1

Tx out

S0

S1

S2

S3

LED

PWM

5 button remote control (Note1)

B4 B3 B2 B1 B0

Note 1:

Up to 15 functions can be implemented by pressing

more than one button simultaneously or by using a

suitable diode array.

+12V

R

+12V

R

(Note 2)

(Note 2)

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

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, fixed 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. 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 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

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