CS8900-CQ3 Cirrus Logic, CS8900-CQ3 Datasheet - Page 33

• Manufacturer Part Number: CS8900-CQ3
• Description: Crystal LAN ISA Ethernet Controller
• Manufacturer: Cirrus Logic

DS271PP3
3.9.5.6 Late Collisions
If a collision is detected after the first 512 bits have
been transmitted, the MAC immediately terminates
transmission, transmits the jam sequence, discards
the packet, and sets the Out-of-window bit (Regis-
ter 8, TxEvent, Bit 9). The CS8900A does not ini-
tiate backoff or attempt to retransmit the frame. For
additional information about Late Collisions, see
Out-of-Window Error in this section.
3.9.5.7 Backoff
After the MAC has completed transmitting the jam
sequence, it must wait, or "Back off", before at-
tempting to transmit again. The amount of time it
must wait is determined by one of two Backoff al-
CS8900A
Crystal LAN™ ISA Ethernet Controller
Ready and Not
in Backoff?
Yes
Fra m e
Tx
Figure 11. Simple Deferral
Yes
Start Monitoring
Network Activity
No
No
Network
Active?
9.6 s
Wait
Transmit
No
Frame
Network
Active?
CIRRUS LOGIC PRODUCT DATA SHEET
Yes
gorithms:
(ISO/IEC 4.2.3.2.5) or the Modified Backoff algo-
rithm. The host selects which algorithm through
the ModBackoffE bit (Register 13, LineCTL,
Bit B).
3.9.5.8 Standard Backoff
The Standard Backoff algorithm, also called the
"Truncated Binary Exponential Backoff", is de-
scribed by the equation:
0 r 2
where r (a random integer) is the number of slot
times the MAC must wait (1 slot time = 512 bit
times), and k is the smaller of n or 10, where n is the
number of retransmission attempts.
3.9.5.9 Modified Backoff
The Modified Backoff is described by the equation:
0
where r (a random integer) is the number of slot
times the MAC must wait, and k is 3 for n < 3 and
k is the smaller of n or 10 for n
number of retransmission attempts.
The advantage of the Modified Backoff algorithm
over the Standard Backoff algorithm is that it re-
duces the possibility of multiple collisions on the
first three retries. The disadvantage is that it ex-
tends the maximum time needed to gain access to
the network for the first three retries.
The host may choose to disable the Backoff algo-
rithm altogether by setting the DisableBackoff bit
(Register 19, TestCTL, Bit B). When disabled, the
CS8900A only waits the 9.6 µs IPG time before
starting transmission.
3.9.5.10 SQE Test
If the CS8900A is transmitting on the AUI, the ex-
ternal transceiver should generate an SQE Test sig-
nal
transmission. The SQE Test is a 10 MHz signal
lasting 5 to 15 bit times and starting within 0.6 to
r 2
on
k
k
the
the
CI+/CI-
Standard
pair
Backoff
following
3, where n is the
algorithm
each
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