PM5381-BI PMC-Sierra, Inc., PM5381-BI Datasheet - Page 558

• Manufacturer Part Number: PM5381-BI
• Description: ATM UNI, Single Channel ATM PHY Interface for 2488.32Mbps
• Manufacturer: PMC-Sierra, Inc.

14.5.2
Proprietary and Confidential to PMC-Sierra, Inc., and for its Customers’ Internal Use
Document ID: PMC-2000489, Issue 4
ROHCLK
TTOHEN
TOHCLK
ROHFP
TOHFP
RTOH
Figure 44 RTOH and ROHFP Output Timing
Transport Overhead Insertion
Figure 45 shows the transmit transport overhead (TTOH) functional timings. TOHCLK is a
20.736 MHz clock generated by gapping a 25.92 MHz clock (33% high duty cycle). 2592 bits
(9x3x12 bytes) are input on TOH between two TOHFP assertions. The 2592 bits is equivalent to
the transport overhead of the first STS-12. Transport overhead insertion is available only for
STS-1 #1 to 12.
Figure 45 TTOH and TTOHEN Input Timing
TTOHEN is used to validate the insertion of the corresponding byte on TTOH. When TTOHEN
is sampled high on the MSB of the byte, the byte will be inserted in the transport overhead. When
TTOHEN is sampled low on the MSB of the byte, the byte is not inserted. TTOH and TTOHEN
are sampled with the rising edge of TOHCLK. TOHFP is aligned with the falling edge of
TOHCLK. The rising edge of TOHCLK should be used to sample TOHFP. Sampling TOHFP
high identifies the MSB of the first A1 byte on TTOH.
When the Transport Overhead Insertion interface is not being used, the TRMP should be set to
use its internal insertion registers (see register description for Register 0081H, 00A1H, 00C1H
and 00E1H).
TTOH
8
7
A1 #1
A1 #1
8
8
A1 #...
A1 #...
8
1
A1 #12
A1 #12
2
3
8
A2 #1
A2 #1
4
S/UNI-2488 Telecom Standard Product Datasheet
5
A1 #1
A1 #1
8
6
A2 #...
A2 #...
7
8
A2 #12
A2 #12
8
8
J0
J0
1
Released
8
2
558