am79c960 Advanced Micro Devices, am79c960 Datasheet - Page 44

• Manufacturer Part Number: am79c960
• Description: Pcnettm-isa Single-chip Ethernet Controller
• Manufacturer: Advanced Micro Devices

1-386
Negative link beat pulses are defined as transmitted sig-
nals with a negative amplitude greater than 585 mV with
a pulse width of 60 ns–200 ns. This negative excursion
may be followed by a positive excursion. This definition
is consistent with the expected received signal at a re-
verse wired receiver, when a link beat pulse which fits
the template of Figure 14–12 in the 10BASE-T Standard
is generated at a transmitter and passed through 100 m
of twisted pair cable.
The polarity detection/correction algorithm will remain
“armed” until two consecutive packets with valid ETD of
identical polarity are detected. When “armed,” the re-
ceiver is capable of changing the initial or previous
polarity configuration according to the detected ETD
polarity.
On receipt of the first packet with valid ETD following re-
set or Link Fail, the T-MAU will use the inferred polarity
information to configure its RXD input, regardless of its
previous state. On receipt of a second packet with a
valid ETD with correct polarity, the detection/correction
algorithm will “lock-in” the received polarity. If the sec-
ond (or subsequent) packet is not detected as
confirming the previous polarity decision, the most re-
cently detected ETD polarity will be used as the default.
Note that packets with invalid ETD have no effect on up-
dating the previous polarity decision. Once two
consecutive packets with valid ETD have been re-
ceived, the T-MAU will lock the correction algorithm until
either a Link Fail condition occurs or RESET is asserted.
During polarity reversal, an internal POL signal will be
active. During normal polarity conditions, this internal
POL signal is inactive. The state of this signal can be
read by software and/or displayed by LED when en-
abled by the LED control bits in the ISA Bus
Configuration Registers (ISACSR5, 6, 7).
Twisted Pair Interface Status
Three signals (XMT, RCV and COL) indicate whether
the T-MAU is transmitting, receiving, or in a collision
state. These signals are internal signals and the behav-
ior of the LED outputs depends on how the LED output
circuitry is programmed.
The T-MAU will power up in the Link Fail state and the
normal algorithm will apply to allow it to enter the Link
Pass state. In the Link Pass state, transmit or receive
activity will be indicated by assertion of RCV signal go-
ing active. If T-MAU is selected using the PORTSEL bits
in CSR15 or MAUSEL pin, then when moving from AUI
to T-MAU selection the T-MAU will be forced into the
Link Fail state.
In the Link Fail state, XMT, RCV and COL are inactive.
AMD
P R E L I M I N A R Y
Am79C960
Collision Detect Function
Activity on both twisted pair signals RXD and TXD
constitutes a collision, thereby causing the COL signal
to be asserted. (COL is used by the LED control cir-
cuits.) The COL will remain asserted until one of the two
colliding signals changes from active to idle. During col-
lision condition, data presented on the DI pair will be
sourced from the RXD input. COL stays active for two
bit times at the end of a collision.
Signal Quality Error (SQE) Test
(Heartbeat) Function
The SQE function is disabled when the 10BASE-T port
is selected and in Link Fail state.
Jabber Function
The Jabber function inhibits the twisted pair transmit
function of the T-MAU if theTXD circuit is active for an
excessive period (20–150 ms). This prevents any one
node from disrupting the network due to a ‘stuck-on’ or
faulty transmitter. If this maximum transmit time is ex-
ceeded, the T-MAU transmitter circuitry is disabled, the
JAB bit is set (CSR4, bit 1), and COL signal asserted.
Once the transmit data stream to the T-MAU is re-
moved, an “unjab” time of 250–750 ms will elapse
before the T-MAU deasserts COL and re-enables the
transmit circuitry.
Power Down
The T-MAU circuitry can be made to go into low power
mode. This feature is useful in battery powered or low
duty cycle systems. The T-MAU will go into power down
mode when RESET is active, coma mode is active, or
the T-MAU is not selected. Refer to the Power Down
Mode section for a description of the various power
down modes.
nal logic of the T-MAU and places the device into power
down mode. In this mode, the Twisted Pair driver pins
(TXD ,TXP ) are asserted LOW, and the internal T-
MAU status signals (LNKST, RCVPOL, XMT, RCV and
COLLISION) are inactive.
Once the SLEEP pin is deasserted, the T-MAU will be
forced into the Link Fail state. The T-MAU will move to
the Link Pass state only after 5 - 6 link beat pulses and/or
a single received message is detected on the RXD
pair.
In snooze mode, the T-MAU receive circuitry will remain
enabled even while the SLEEP pin is driven LOW.
The T-MAU circuitry will always go into power down
mode if RESET is asserted, coma mode is enabled, or
the T-MAU is not selected.
Any of the three conditions listed above resets the inter-