
PRELIMINARY
XRT86SH221
64
REV. P1.0.5
SDH-TO-PDH FRAMER/MAPPER WITH INTEGRATED 21-CHANNEL E1 SH LIU
HARDWARE RDI-L INSERTION
Hardware can enable RDI-L insertion by setting the most significant bit of the B2 byte to "1" on the TTOH serial
input line. Note that software must first enable hardware RDI-L insertion. The state of the TTOHIns pin has no
effect during the B2 slots.
TXSTOH_CONT BLOCK
The txstoh_proc has one 8 bit internal data bus interface. The txstoh_cont block provides the register file and
internal processor interface for the transport section of the SDH transmitter. It selects the value of the transport
overhead bytes from either hardware or software according to the control registers and forwards them to the
txstoh_proc block for transmission. The hardware value is specified through a parallel data input port. If the
transport overhead bytes are serially entered into the chip, it is assumed that a serial to parallel data converter
has converted the data to parallel format and has placed the data on the input of the txstoh_cont block at the
appropriate instances during transmission. The txstoh_cont also provides control for the transmission of a
section trace message (J0 byte).
A1/A2 GENERATION
The txstoh_cont block generates alternate A1 and A2 values based on hardware or software requests and
sends them to the txstoh_proc block via the tx_toh_data lines. The txstoh_cont block accepts A1/A2 values
from the hardware input, or alternatively, software can specify an error mask indicating the A1/A2 bytes in
which errors should be inserted for diagnostic purposes. A1/A2 errors are always inserted on frame
boundaries, i.e., the A1/A2 error mask is only sampled at the start of every frame.
B1 ERROR MASK GENERATION
The txstoh_cont block allows software to insert errors into the B1 value calculated and transmitted by the
txstoh_proc block. By writing to an appropriate register bit, a software controlled error mask is used to insert
errors into the B1 byte.
B2 ERROR MASK GENERATION
The txstoh_cont block allows software to control B2 BER generation through two registers: A byte error mask
register and a bit error mask register. The byte error mask specifies which of the B2 bytes are to be corrupted
and the bit error mask specifies which bits are to be inverted in the B2 bytes that are to be corrupted. In the
case of an 8 bit internal data bus, each bit in the B2 byte error mask corresponds to 4 bytes (i.e., one time slot).
The B2 byte and bit error masks are sampled before the first B2 byte of each frame if B2 error insertion is
enabled by software.
SCRAMBLING
The txstoh_cont block allows software to disable scrambling by setting a bit in the control register. Otherwise,
the SDH data is scrambled using the identical algorithm as the de-scrambling process.
K1/K2 CONTROL
The K1/K2 bytes contain the APS code. The APS code transmitted either come from software registers or from
hardware via the TxOH serial pin. Note that the 3 least significant bits of the K2 byte (bits 6, 7 and 8) may be
overridden by an RDI-L alarm.
RDI-L CONTROL (K2 BITS 6, 7, AND 8)
The RDI-L indication bits consist of the 3 least significant bits of the K2 byte. The bits usually contain portions
of the transmitted APS code. However, they are overridden with the RDI-L pattern 3'b110 if any of the following
software configurable conditions occur: LOS, LOF, or AIS-L. RDI-L can also be inserted from hardware via the
TxOH serial pin or forced by software. RDI-L insertion is done according to the following SDH rules:
I
TE shall generate RDI-L within 125
μ
s of detecting an AIS-L defect (or a lower-layer, traffic-related, near-
end defect). The LTE shall generate RDI-L by inserting the code '110' in bits 6, 7, and 8 of the K2 byte.
The lower-layer, traffic-related, near-end defects referred to by R6-200 are LOS and LOF from the receiver
blocks.