CS8900-IQ View Datasheet(PDF) - Cirrus Logic
Part Name
Description
MFG CO.
CS8900-IQ Datasheet PDF : 138 Pages
| |||
CS8900A
Crystal LAN™ ISA Ethernet Controller
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-
Start Monitoring
Network Activity
Yes Network
Active?
No
Wait
9.6 µs
Tx
Frame
No
Ready and Not
in Backoff?
No
Network Yes
Active?
Yes
Transmit
Frame
Figure 11. Simple Deferral
gorithms: the Standard Backoff algorithm
(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 ≤ 2k
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 ≤ r ≤ 2k
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 ≥ 3, where n is the
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 on the CI+/CI- pair following each
transmission. The SQE Test is a 10 MHz signal
lasting 5 to 15 bit times and starting within 0.6 to
CIRRUS LOGIC PRODUCT DATASHEET
32
DS271PP4
Share Link: 