HCS200 datasheet(7/34 Pages) MICROCHIP

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DS40138D-page 7

HCS200

checked against the receiver’s stored value to verify

that the decryption process was valid. If the discrimi-

nation value was programmed as the 12 LSb’s of the

serial number then it may merely be compared to the

respective bits of the received serial number; saving

EEPROM space.

3.6.2

BAUD RATE SELECT BIT (BSL0)

BSL0 selects the speed of transmission and the code

word blanking. Table 3-3 shows how the bit is used to

select the different baud rates and Section 5.2 provides

detailed explanation in code word blanking.

TABLE 3-3:

BAUD RATE SELECT

3.6.3

LOW VOLTAGE TRIP POINT

SELECT (VLOW SEL)

The low voltage trip point select bit tells the HCS200

what VDD level is being used. This information will be

used by the device to determine when to send the volt-

age low signal to the receiver. When this bit is set to a

one, the VDD level is assumed to be operating from a

9.0 volt or 12.0 volt VDD level. If the bit is set to zero,

the VDD level is assumed to be 6.0 volts. Refer to

Figure 3-1 for voltage trip point.

FIGURE 3-1:

VOLTAGE TRIP POINTS

BY CHARACTERIZATION

4.0

TRANSMITTED WORD

4.1

Code Word Format

The HCS200 code word is made up of several parts

(Figure 4-1). Each code word contains a 50% duty

cycle preamble, a header, 32 bits of encrypted data and

34 bits of fixed data followed by a guard period before

another code word can begin. Refer to Table 9-3 for

code word timing.

4.2

Code Word Organization

The HCS200 transmits a 66-bit code word when a

button is pressed. The 66-bit word is constructed from

a Fixed Code portion and an Encrypted Code portion

(Figure 4-2).

The 32 bits of Encrypted Data are generated from 4

button bits, 12 discrimination bits and the 16-bit sync

value. The encrypted portion alone provides up to four

billion changing code combinations.

The 34 bits of Fixed Code Data are made up of 1 sta-

tus bit, 1 fixed bit, 4 button bits and the 28-bit serial

number. The fixed and encrypted sections combined

increase the number of code combinations to 7.38 x

1019.

4.3

Synchronous Transmission Mode

Synchronous Transmission mode can be used to clock

the code word out using an external clock.

To enter Synchronous Transmission mode, the Pro-

gramming mode start-up sequence must be executed

as shown in Figure 4-3. If either S1 or S0 is set on the

falling edge of S2, the device enters Synchronous

Transmission mode. In this mode it functions as a nor-

mal transmitter, with the exception that the timing of the

PWM data string is controlled externally and that 16

extra reserved bits are transmitted at the end of the

code word. The reserved bits can be ignored. The but-

ton code will be the S0, S1 value at the falling edge of

S2. The timing of the PWM data string is controlled by

supplying a clock on S2 and should not exceed 20 kHz.

When in Synchronous Transmission mode S2 should

not be toggled until all internal processing has been

completed as shown in Figure 4-3.

BSL0

Basic Pulse

Element

Code Words

Transmitted

400

μsAll

200

μs

1 out of 2

-40

100

8.5

7.5

8.0

7.0

9.0

VLOW

Temp (C)

Volts (V)

VLOW SEL = 1

-20

2.5

3.0

3.5

4.0

VLOW SEL = 0

4.5

5.0

5.5

Max

Min

Max

Min

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