HCS300-SLASHP datasheet(7/28 Pages) MICROCHIP

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DS21137F-page 7

HCS300

3.6

CONFIG (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

as the status of option configurations. The following

sections further explain these bits.

TABLE 3-2:

CONFIGURATION WORD

3.6.1

DISCRIMINATION VALUE

(DISC0 TO DISC9)

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.

3.6.2

OVERFLOW BITS

(OVR0, OVR1)

The overflow bits are used to extend the number of

possible 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

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

BAUD RATE 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 5.7 provides detailed explanation in code word

blanking.

TABLE 3-3:

BAUD RATE SELECT

3.6.4

LOW VOLTAGE TRIP POINT

SELECT (VLOW SEL)

The low voltage trip point select bit is used to tell the

HCS300 what VDD level is being used. This information

will be used by the device to determine when to send

the voltage low signal to the receiver. When this bit is

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

from a 5V or 6V VDD level. If the bit is set low, then the

VDD

level is assumed to be 3.0 volts.

FIGURE 3-1:

VLOW CHARACTERISTICS

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 (VLOW

SEL

)

Baud rate Select Bit 0 (BSL0)

Baud rate Select Bit 1 (BSL1)

Reserved, set to 0

BSL1

BSL0

Basic Pulse

Element

Code Words

Transmitted

400

µsAll

200

µs

1 out of 2

100

µs

1 out of 2

100

µs

1 out of 4

-40

050

2.0

1.6

1.8

1.4

2.2

2.4

2.6

3.6

3.8

4.0

4.2

VLOW

Temp (C)

Volts (V)

VLOW sel = 0

VLOW sel = 1

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