PM7366-PI datasheet(46/286 Pages) PMC

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RELEASED

PM7366 FREEDM-8

DATA SHEET

PMC-1970930

ISSUE 4

FRAME ENGINE AND DATA LINK MANAGER

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

FUNCTIONAL DESCRIPTION

9.1

High-Level Data Link Control Protocol

Figure 1 shows a diagram of the synchronous HDLC protocol supported by the FREEDM-8. The

incoming stream is examined for flag bytes (01111110 bit pattern) which delineate the opening and

closing of the HDLC packet. The packet is bit de-stuffed which discards a "0" bit which directly

follows five contiguous "1" bits. The resulting HDLC packet size must be a multiple of an octet (8

bits) and within the expected minimum and maximum packet length limits. The minimum packet

length is that of a packet containing two information bytes (address and control) and FCS bytes.

For packets with CRC-CCITT as FCS, the minimum packet length is four bytes while those with

CRC-32 as FCS, the minimum length is six bytes. An HDLC packet is aborted when seven

contiguous "1" bits (with no inserted "0" bits) are received. At least one flag byte must exist

between HDLC packets for delineation. Contiguous flag bytes, or all ones bytes between packets

are used as an "inter-frame time fill". Adjacent flag bytes may share zeros.

Figure 1 – HDLC Frame

Flag

Information

FCS

Flag

HDLC Packet

Flag

The CRC algorithm for the frame checking sequence (FCS) field is either a CRC-CCITT or CRC-

32 function. Figure 2 shows a CRC encoder block diagram using the generating polynomial g(X)

= 1 + g1X + g2X2 +…+ gn-1Xn-1 + Xn. The CRC-CCITT FCS is two bytes in size and has a

generating polynomial g(X) = 1 + X5 + X12 + X16. The CRC-32 FCS is four bytes in size and has

a generating polynomial g(X) = 1 + X + X2 + X4 + X5 + X7 + X8 + X10 + X11 + X12 + X16 + X22

+ X23 + X26 + X32. The first FCS bit received is the residue of the highest term.

Figure 2 – CRC Generator

Dn-1

Message

Parity Check Digits

gn-1

LSB

MSB

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