8101 datasheet(48/172 Pages) LSI

48 / 172 page

2-30

Functional Description

2.11.4 End Of Packet

The End of Packet Delimiter, referred to as EPD indicates the end of a

packet. The EPD consists of two codes, /T/ and /R/, inserted at the end

of the packet, as deﬁned in IEEE 802.3z and shown in Table 2.8, and

also shown in Figure 2.3. To maintain synchronization on the proper word

boundaries, an outgoing packet must also have an even number of 10-bit

words transmitted. If the packet has an odd number of 10-bit words

transmitted after the /T/R/ codes, an extra /R/ code is inserted after the

/T/R/ (now a /T/R/R/) to meet the even word requirement, as deﬁned in

IEEE 802.3z and shown in Figure 2.3.

The transmit 8B10B PCS section appends either the /T/R/ or /T/R/R/

codes to the end of each transmit packet.

The receive 8B10B PCS section constantly monitors the incoming 10B

bitstream. If the /T/R/ codes are detected, the end of packet indication is

given to the receive MAC, and the /T/R/ or /T/R/R/ codes are stripped

from the end of the packet. If the 8B10B PCS receiver detects the

transition from the nonidle pattern to an idle pattern (/I/ code stream)

without intervening /T/R/ codes, the packet is assumed to have a bad

EPD. Packets with a bad EPD are discarded if the controller is so

programmed. Refer to Section 2.13, “Packet Discard” for more details on

discards. Clearing the DIS_CWRD bit in “Register 8–Conﬁguration 2‚"

Section 4.3.9, programs the controller to not discard packets with PCS

errors.

2.11.5 Idle

The interpacket gap time is ﬁlled with a continuous stream of codes

referred to as the idle pattern. The idle pattern consists of a continuous

stream of /I2/ codes, as deﬁned in IEEE 802.3z and shown in Figure 2.3.

The running disparity during idle is deﬁned to be negative. So, if the

running disparity after the last /R/ code of a packet is positive, a single

/I1/ code must be transmitted as the ﬁrst idle code to make the running

disparity negative. All subsequent idle codes must be /I2/, as deﬁned in

IEEE 802.3z and shown in Figure 2.3. The /I1/ and /I2/ codes are deﬁned

in Table 2.8.

The transmit 8B10B PCS section inserts a continuous stream of

/I1/I2/I2/I2/

…or /I2/I2/I2/I2/…codes between packets.

8101 Datasheet(PDF) 48 Page - LSI Computer Systems