ort8850 Lattice Semiconductor Corp., ort8850 Datasheet - Page 14

• Manufacturer Part Number: ort8850
• Description: Field-programmable System Chip Fpsc Eight-channel X 850 Mbits/s Backplane Transceiver
• Manufacturer: Lattice Semiconductor Corp.

Lattice Semiconductor
SONET Framing
Each 850 Mbits/s serial link uses a pseudo-SONET protocol. SONET A1/A2 framing is used on the link to detect
the 8 kHz frame location. The link is also scrambled using the standard SONET scrambler definition to ensure
proper transitions on the link for improved CDR performance. The ORT8850 can do SONET framing and scram-
bling in both STS-12 and STS-3 formats.
Elastic buffers (FIFOs) are used to align each incoming STS-12 link to the local 77.76 MHz clock and 8 kHz frame.
These FIFOs will absorb delay variations between the eight channels due to timing skews between cards and
along backplane traces. For greater variations, a streamlined pointer processor (pointer mover) within the STM
macro will align the 8 kHz frames regardless of their incoming frame position.
The data rates for SONET are covered in the following table. Values that fall in between those shown in the table for
each mode are supported (126.00 Mbits/s - 212.50 Mbits/s, 504.00 Mbits/s - 850.00 Mbits/s). 63.00 MHz is the
slowest reference clock while 106.25 MHz is the fastest reference clock frequency supported.
Table 2. Supported SONET Data Rates
An STS-N frame can be broadly divided into the Transport Overhead (TOH) and the Synchronous Payload Enve-
lope (SPE) areas. The TOH comprises of bytes that are used for framing, error detection and various other func-
tions. The start of the SPE can begin at any point in a SONET frame. The start of the SPE is determined using the
pointer bytes located in the TOH. The basic STS-1 frame is shown in Figure 4. Higher rate STS_N signals are cre-
ated by byte interleaving N STS-1 signals. Some TOH bytes have slightly different functions in STS-N frames than
in the basic STS-1 frame. The ORT8850 offers both a transparent option and a serial insertion option for process-
ing the TOH bytes.
Figure 4. STS-1 Frame Format
106.25 MHz
Reference
77.76 MHz
63 MHz
Clock
9 rows
3 columns
Overhead
Transport
(TOH)
504.00 Mbits/s
622.08 Mbits/s
850.00 Mbits/s
STS-12 Mode
Synchronous
14
90 columns
(SPE)
Payload Envelope
126.00 Mbits/s
155.52 Mbits/s
212.50 Mbits/s
STS-3 Mode
ORCA ORT8850 Data Sheet