HC-5560 Datasheet, PDF (5/9 Pages) Intersil Corporation – PCM Transcoder

HC-5560
with N Zero Substitution. B6ZS is used commonly in North
American T2 (6.3212MHz) carriers. For every string of 6
zeros, bipolar code is substituted according to the following
rule:
If the immediate preceding pulse is of (-) polarity, then
code each group of 6 zeros as 0+- 0+-, and if the
immediate preceding pulse is of (+) polarity, code each
group of 6 zeros as 0+- 0-+.
One can see the consecutive logic 1 pulses of the same
polarity violate the AMI coding scheme.
e.g.,
6
PCM CODE
0 0 0 1 0 1 110 0 0 0 0 0 1
0 ^- +0 + -
B6ZS (-)
V
V
0+-0 - +
B6ZS (+)
V = VIOLATION
V
V
B8ZS is used commonly in North American T1 (1.544MHz)
and T1C (3.152MHz) carriers. For every string of 8 zeros,
bipolar code is substituted according to the following rules:
1. If the immediate preceding pulse is of (-) polarity, then
code each group of 8 zeros as 000-+ 0+-.
2. If the immediate preceding pulse is of (+) polarity then
code each group of 8 zeros as 000+-0-+.
e.g.,
8
PCM CODE
1 0 10 0 0 0 0 0 0 0 1 1 0
B8ZS (-)
00 0 - +0+ -
V
V
B8ZS (+)
0 0 0 + ^-0 ^- +
V
V = VIOLATION
The BNZS coding schemes, in addition to eliminating DC
wander, minimize timing jitter and allow a line error monitor-
ing capability.
Another coding scheme is HDB3, high density bipolar 3, used
primarily in Europe for 2.048MHz and 8.448MHz carriers. This
code is similar to BNZS in that it substitutes bipolar code for 4
consecutive zeros according to the following rule:
1. If the polarity of the immediate preceding pulse is (-)
and there have been an odd (even) number of logic 1
pulses since the last substitution, each group of 4 con-
secutive zeros is coded as 000-(+00+).
2. If the polarity of the immediate preceding pulse is (+)
then the substitution is 000+(-00-) for odd (even) num-
ber of logic 1 pulses since the last substitution.
e.g.,
4
4
PCM CODE
0 0 0 0 1 01 11 0 0 0 0 0 0 1
HDB3 (-)
000 -
V
+ 0 0+
V
HDB3 (+)
000 +
V
- _{0 0}-
V
V = VIOLATION
The 3 in HDB3 refers to the coding format that precludes
strings of zeros greater than 3. Note that violations are pro-
duced only in the fourth bit location of the substitution code
and that successive substitutions produce alternate polarity
violations.
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