HCS201 datasheet(7/36 Pages) MICROCHIP

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DS41098D-page 7

HCS201

3.3

Reserved

Must be initialized to 0000H.

3.4

SER_0, SER_1

(Encoder Serial Number)

SER_0 and SER_1 are the lower and upper words of

the device serial number, respectively. Although there

are 32 bits allocated for the serial number, only the

lower order 28 bits are transmitted. The serial number

is meant to be unique for every transmitter.

3.5

SEED_0, SEED_1 (Seed Word)

The 2-word (32-bit) seed code will be transmitted when

all three buttons are pressed at the same time (see

Figure 4-2). This allows the system designer to imple-

ment the secure learn feature or use this fixed code

word as part of a different key generation/tracking pro-

cess.

TABLE 3-2:

DISCRIMINATION WORD

3.6

DISC

(Discrimination Word)

The discrimination value aids the post-decryption

check on the decoder end. It may be any value, but in

a typical system it will be programmed as the 12 Least

Significant bits of the serial number. Values other than

this must be separately stored by the receiver when a

transmitter is learned. The discrimination bits are part

of the information that form the encrypted portion of

the transmission (Figure 4-2). After the receiver has

decrypted a transmission, the discrimination bits are

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.

3.7

CONFIG

(Configuration Word)

The Configuration Word is a 16-bit word stored in

EEPROM array that is used by the device to store infor-

mation used during the encryption process, as well as

the status of option configurations. Further explana-

tions of each of the bits are described in the following

sections.

TABLE 3-3:

CONFIGURATION WORD

3.7.1

OSCILLATOR TUNING BITS

(OSC0 AND OSC3)

These bits are used to tune the frequency of the

HCS201 internal clock oscillator to within ±10% of its

nominal value over temperature and voltage.

3.7.2

LOW VOLTAGE TRIP POINT

SELECT (VLOWS)

The low voltage trip point select bit (VLOWS) and the S3

setting bit (S3SET) are used to determine when to send

the VLOW signal to the receiver.

* See also Section 3.7.6

Bit Number

Bit Description

Discrimination Bit 0

Discrimination Bit 1

Discrimination Bit 2

Discrimination Bit 3

Discrimination Bit 4

Discrimination Bit 5

Discrimination Bit 6

Discrimination Bit 7

Discrimination Bit 8

Discrimination Bit 9

Discrimination Bit 10

Discrimination Bit 11

Not Used

Bit Number

Bit Name

0OSC0

1OSC1

2OSC2

3OSC3

4VLOWS

5BRS

6MTX4

TXEN

S3SET

XSER

Not Used

TABLE 3-4:

TRIP POINT SELECT

VLOWS

S3SET*

Trip Point

4.4

6.75

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