HCS301 datasheet(6/20 Pages) MICROCHIP

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HCS301

DS21143A-page 6

Preliminary

3.6

Conﬁguration Word

The conﬁguration word is a 16-bit word stored in

EEPROM array that is used by the device to store

information used during the encryption process, as well

the

status

option

conﬁgurations. Further

explanations of each of the bits are described in the

following sections.

TABLE 3-2:

CONFIGURATION WORD

3.6.1

DISCRIMINATION VALUE

(DISC0 TO DISC9)

The discrimination value can be programmed with any

value to serve as a post decryption check on the

decoder end. In a typical system, this will be

programmed with the 10 least signiﬁcant bits of the

serial number or a constant value, which will also be

stored by the receiver system after a transmitter has

been learned. The discrimination bits are part of the

information that is to form the encrypted portion of the

transmission. After the receiver has decrypted a trans-

mission, the discrimination bits can be checked against

the stored value to verify that the decryption process

was valid.

3.6.2

OVERFLOW BITS (OVR0 AND OVR1)

The overﬂow bits are used to extend the number of pos-

sible synchronization values. The synchronization

counter is 16 bits in length, yielding 65,536 values

before the cycle repeats. Under typical use of

10 operations a day, this will provide nearly 18 years of

use before a repeated value will be used. Should the

system designer conclude that is not adequate, then

the overﬂow bits can be utilized to extend the number of

unique values. This can be done by programming

OVR0 and OVR1 to 1s at the time of production. The

encoder will automatically clear OVR0 the ﬁrst time that

the synchronization value wraps from 0xFFFF to

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

Overﬂow Bit 0 (OVR0)

Overﬂow Bit 1 (OVR1)

Low Voltage Trip Point Select

Baudrate Select Bit 0 (BSL0)

Baudrate Select Bit 1 (BSL1)

Envelope Encryption Select (EENC)

0x0000 and clear OVR1 the second time the counter

wraps. Once cleared, OVR0 and OVR1 cannot be set

again, thereby creating a permanent record of the

counter overﬂow. This prevents fast cycling of 64K

counter. If the decoder system is programmed to track

the overﬂow bits, then the effective number of unique

synchronization values can be extended to 196,608.

3.6.3

ENVELOPE ENCRYPTION (EENC)

If the EENC bit is set to a 1, the serial number and func-

tion code will also be encrypted so that it will appear to

be random. The 16-bit envelope key and envelope algo-

rithm will be used for encryption.

3.6.4

BAUDRATE SELECT BITS (BSL0, BSL1)

BSL0 and BSL1 select the speed of transmission and

the code word blanking. Table 3-3 shows how the bits

are used to select the different baud rates and

Section 5.2 provides detailed explanation in code word

blanking.

TABLE 3-3:

BAUDRATE SELECT

BSL1

BSL0

Basic Pulse

Element

Code Words

Transmitted

400

µs

All

200

µs

1 out of 2

100

µs

1 out of 2

100

µs

1 out of 4

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