73

Definition of HDB3 Code Used in CD22103A HDB3

Transcoder (As Per CCITRT G703 Annex

Recommendations) and Error Detection

Coding Of A Binary Signal Into An HDB3 Signal Is Done

According To The Following Rules:

1. HDB3 signal is pseudoternary; the three states are

denoted B+, B-, and 0.

2. Spaces (zeros) in the binary NRZ signal are coded as

spaces in the HDB3 signal. For strings of four spaces,

however, special rules apply (See Item 4 below).

3. Marks (ones) in the binary signal are coded alternately as

B+ and B- in the HDB3 signal (alternate mark inversion).

Violations of the rule of alternate mark inversion are intro-

duced when coding strings of four spaces (See Item 4

below).

4. Strings of four spaces in the binary signal are coded

according to the followinq rules:

A. The first space of a string is coded as a space if the polar-

ity of the preceding mark of the HDB3 signal has a polarity

opposite to the preceding violation and is not a violation by

itself; it is coded as a mark, i.e., not a violation (i.e., B+ or

B-), if the preceding mark of the HDB3 signal has the same

polarity as that of the preceding violation or is by itself a

violation.

This rule ensures that successive violations are of alter-

nate polarity so that no DC component is introduced.

B. The second and third spaces of a string are always coded

as spaces.

C. The last space of a string of four is always coded as a

mark, the polarity of which is such that it violates the rule of

alternate mark inversion. Such violations are denoted V+

or V- according to their polarity.

FIGURE 5. CRX RECONSTRUCTION REQUIREMENTS

FIGURE 6. RECEIVER ALARM-INHIBIT-SIGNALS TIMING WAVEFORMS

FIGURE 7. RECEIVER ERROR-SIGNALS TIMING WAVEFORMS

CKR

CRX

50%

50%

τ

τ

CRX

NRZ - OUT DATA

RAIS

AIS

CRX

+HDB3 IN

-HDB3 IN

ERR

CD22103A