PM5345 datasheet(69/196 Pages) PMC

69 / 196 page

PM5345 S/UNI-155

DATA SHEET

PMC-930305

ISSUE 4

SATURN USER NETWORK INTERFACE

PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA, INC., AND FOR ITS CUSTOMERS’ INTERNAL USE

10.14.1

Idle/Unassigned Cell Generator

The Idle/Unassigned Cell Generator inserts idle or unassigned cells into the cell

stream when enabled. Registers are provided to program the GFC, PTI, and

CLP fields of the idle cell header and the idle cell payload. The idle cell HCS is

automatically calculated and inserted.

10.14.2

Scrambler

The Scrambler scrambles the 48 octet information field. Scrambling is performed

using a parallel implementation of the self synchronous scrambler described in

the references. The cell headers are transmitted unscrambled, and the

scrambler may optionally be completely disabled.

10.14.3

HCS Generator

The HCS Generator performs a CRC-8 calculation over the first four header

octets. A parallel implementation of the polynomial, x8+x2+x+1 is used. The

coset polynomial, x6+x4+x2+1 is added (modulo 2) to the residue. The HCS

Generator optionally inserts the result into the fifth octet of the header.

10.14.4

Transmit FIFO

The Transmit FIFO provides FIFO management and the asynchronous interface

between the S/UNI device and the external environment. The transmit FIFO can

accommodate four cells. It provides for the separation of the STS-3c line or

physical layer timing from the ATM layer timing.

The FIFO supports two data structures. The first data structure consists of 27

16-bit words comprising the 5 octet cell header and the 48 octet payload (the

HCS byte, along with the header error insertion control, is passed in this

structure). Note that the header error insertion control allows the programmable

insertion of one or more bit errors in the HCS octet. The second data structure

consists of 53 8-bit words, comprising the 5 octet cell header, and the 48 octet

payload.

Management functions include filling the transmit FIFO, indicating when cells are

available to be written to the transmit FIFO, maintaining the transmit FIFO read

and write pointers, and detecting a FIFO overrun condition.

Upon detection of an overrun condition, the FIFO is automatically reset. The four

cells contained in the overrun FIFO are flushed. Typically, one of the four cells is

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