2.0 Functional Description
CN8223
2.3 Overhead Generation
ATM Transmitter/Receiver with UTOPIA Interface
Table 2-12. STS-1, STS-3c, and STM-1 Overhead Values (2 of 2)
Overhead Byte
CN8223 Operation
H4
This byte is no longer used by the CN8223. Its value is insignificant. H4 is the number of octets
between the H4 octet position and the next cell starting position in the payload and thus has a value
ranging from 0 to 52. Its value will change in each frame because the payload does not hold an
integral number of cells. This used to be the mechanism to locate cell boundaries but is no longer
used since the HEC alignment technique was developed. Thus, the value in this position does not
really matter. The CN8223 transmitter still generates this value but the receiver does not pay
attention to it.
B2
Calculates and inserts B2. Errors can be inserted using the TXFEAC_ERRPAT register. Allows single
error insertion or all-zero value (continuous error).
K1, K2
The K1 and K2 (FERF) values are internally generated through register 0x32. They can also be
inserted externally through port TXOVH[7:0].
D4–D12
Z1
Always inserted through port TXOVH[7:0].
Always inserted through port TXOVH[7:0].
M1
Calculates and inserts line FEBE, based on incoming B2 errors. Can be set for FEBE = all 1s or all 0s.
Always inserted through port TXOVH[7:0].
E2
J1
Always inserted through port TXOVH[7:0].
B3
Calculates and inserts B3. Errors can be inserted using the TXFEAC_ERRPAT register. Allows single
error insertion or all-zero value (continuous error).
C2
G1
Three options:
•
•
•
If disabled, value = 0x00
Can be internally generated (0x13)
Can be externally inserted through port TXOVH[7:0]
Calculates and inserts path FEBE (or all 1s or all 0s). Inserts path RDI and qualifier (path yellow). If
disabled, inserts value of 0x00.
F2
Always inserted through port TXOVH[7:0].
Always inserted through port TXOVH[7:0].
Always inserted through port TXOVH[7:0].
Z3, Z4
Z5
2-16
Conexant
100046C
CONEXANT [ CONEXANT SYSTEMS, INC ]
