SCS152 データシートの表示（PDF） - Microchip Technology

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SCS152

KEELOQ Token Card Chip

Microchip Technology 

SCS152

2.4 Digit Fields

2.4.1 DIGIT FIELD VALUE

Each digit field, D4 to D0, represents a number equal to

the number of ‘1’ bits in the field. Table 2-2 shows the

value of the digit field for each legal digit value.

TABLE 2-2: DIGIT FIELD VALUES

Digit Value

Field Value

0

0000 0000

1

1000 0000

2

1100 0000

3

1110 0000

4

1111 0000

5

1111 1000

Note:

6

1111 1100

7

1111 1110

8

1111 1111

The bits are shown, right to left, in the order

in which they are read out.

2.4.2 TOKEN COUNTER VALUE

Note: The value digit D4 is shown in the formulas as |D4| indicating the number of 1 bits in the digit D4 field.

Similarly |D3| indicates the number of 1 bits in the digit D3 field, and so on.

The following formula shows how the digit fields combine to form the token counter value:

Tokens = D4 × 4096 + D3 × 512 + D2 × 64 + D1 × 8 + D0

This is, in fact, an octal representation of a value and can be written as:

Tokens = D4 × 84 + D3 × 83 + D2 × 82 + D1 × 81 + D0 × 80

Suppose the 5-digit field contain the values: (D4=3), (D3=0), (D2=7), (D1=1), (D0=3). The token counter value is then

307138 in octal or in decimal:

Tokens = 3 × 4096 + 0 × 512 + 7 × 64 + 1 × 8 + 3 = 1274710

A digit needs to be set to eight to handle the borrow from the next higher stage. This also implies that each counter value

does not have a unique representation. For example, 005008 = 5 x 64 = 32010 or 004808 or 004788.

© 1997 Microchip Technology Inc.

Preliminary

DS40150B-page 3

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