HCS361 datasheet(4/24 Pages) MICROCHIP

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HCS361

DS40146C-page 4

Preliminary

2.0

DEVICE OPERATION

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

the HCS361 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

The high security level of the HCS361 is based on the

patented KEELOQ technology. A block cipher type of

encryption algorithm 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

one bit from the information in the previous transmis-

sion, the next coded transmission will be totally differ-

ent. Statistically, if only one bit in the 32-bit string of

information changes, approximately 50 percent of the

coded transmission will change. The HCS361 will wake

up upon detecting a switch closure and then delay

approximately 6.5 ms for switch debounce (Figure 2-2).

The synchronization information, 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 a button is

pressed, even if the same button is pushed again.

Keeping a button pressed for a long time will result in

the same code word being transmitted until the button

is released or time-out occurs. 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 oper-

ations per day. Overﬂow information programmed into

the encoder can be used by the decoder to extend the

number of unique transmissions to more than 128K.

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

which case the current code word will be completed

and the power down will occur.

VDD

Tx out

LED

VDD

PWM

VSS

2 button remote control

VDD

Tx out

LED

VDD

PWM

VSS

5 button remote control (Note)

B4 B3 B2 B1 B0

Note:

Up to 15 functions can be implemented

by pressing more than one button simul-

Name

Number

Description

Switch input 0

Switch input 1

Switch input 2/Can also be clock

pin when in programming mode

Switch input 3/Clock pin when in

programming mode

VSS

Ground reference connection

PWM

Pulse width modulation (PWM)

output pin/Data pin for

programming mode

LED

Cathode connection for directly

driving LED during transmission

VDD

Positive supply voltage

connection

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