PM5381-BI PMC-Sierra, Inc., PM5381-BI Datasheet - Page 524

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PM5381-BI

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

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13.5.1
13.5.2
Proprietary and Confidential to PMC-Sierra, Inc., and for its Customers’ Internal Use
Document ID: PMC-2000489, Issue 4
Figure 28 A 63 Byte Packet Data Structure
Both the start of the packet and the end of the packet must be identified by the TSOP/RSOP and
TEOP/REOP signals. When the first section of a packet is transferred over the interface, the
TSOP/RSOP signals will be high for Byte 1 of the packet only. The TMOD[1:0] pins will
indicate how many bytes of the final word are valid. Bits 31 to 24 form the first transmitted byte
and bit 31 is the bit which is transmitted first.
Limitation When Using Externally Generated FCS In STS-48c Mode
When the S/UNI-2488 is set up in STS-48c POS mode and FCS bytes are passed through the
transmit POS-PHY L3 interface, the overall throughput is reduced. The maximum bandwidth
throughput will be reduced by a maximum of 2 bytes per packet. The overall effect will depend
on the length of the packets + FCS bytes being transferred through the POS-PHY L3 interface. If
the packet + FCS length is evenly divisible by 4 bytes, no bandwidth is lost for that packet.
Limitations From Small Packets
The S/UNI-2488 cannot handle packet payloads (excluding FCS) which are smaller than 4 bytes.
In the receive direction, the RCFP should be programmed such that the minimum packet size is at
least 4 bytes + FCS. Packet payloads of size 3 bytes or less are tagged by the RCFP packet
processor and marked as minimum length violations. For the case where the FCS is passed
through the PL3 bus, the min size (packet + FCS) must be at least 5 bytes.
In the transmit direction, the minimum packet payload size permitted is 4 bytes. The exception to
this is when the packet is aborted by use of the TERR pin. Aborted packets can be less than the 4
byte minimum. The S/UNI-2488 will extend these packets to 4 bytes before tagging with the
appropriate abort sequence.
Word 1
Word 2
Word 3
.
.
.
Word 15
Word 16
Bit 31
Byte 1/SOP
Byte 5
Byte 9
.
.
.
Byte 57
Byte 61
Byte 2
Byte 6
Byte 10
.
.
.
Byte 58
Byte 62
Bit 16
S/UNI-2488 Telecom Standard Product Datasheet
Bit 15
Byte 3
Byte 7
Byte 11
.
.
.
Byte 59
Byte 63/EOP
Byte 4
Byte 8
Byte 12
.
.
.
Byte 60
Unused
Bit 0
Released
524

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