AM79C850KCW AMD [Advanced Micro Devices], AM79C850KCW Datasheet - Page 16

• Manufacturer Part Number: AM79C850KCW
• Description: SUPERNET-R 3
• Manufacturer: AMD [Advanced Micro Devices]

These signals communicate to the host the current
condition of the transmit queues. This provides useful
information for doing the host interface. The meaning of
these states are as follows:
A. QCTRL[2:0] = 000
The quiescent state exists when SUPERNET 3 is
neither transmitting nor receiving. This state is also true
while loading a transmit queue (making a write request
to a queue) and not yet unloading it, and when there is
space in the queue for more data.
B. QCTRL[2:0] = 001, 010 or 011
These states indicate unloading frame from the Syn-
chronous Queue, Asynchronous Queue 0 or Asynchro-
nous Queue 1, respectively. They are valid as long as
the corresponding queue is not yet in the almost full or
full state and, at the same time, the SUPERNET 3 is
reading out of the queue. The host can transfer more
data into the corresponding queue when any of these
states is present. These three combinations may
appear one BMCLK period later than the time indicated
in the timing diagram.
C. QCTRL[2:0] = 101
This state is present when all of the following three
conditions are satisfied:
1. The host has issued a write request for this queue
2. Transmit FIFO underrun occurs
3. Transmit buffer-memory underrun occurs for
D. QCTRL[2:0] = 110
When the transmit queue being requested is full, this
state is presented at the queue control signals. Note that
16
QCTRL2
this queue
0
0
0
0
1
1
1
1
AMD
QCTRL1
0
0
1
1
0
0
1
1
QCTRL0
0
1
0
1
0
1
0
1
Indicated Status
(1) Quiescent.
(2) Space remains
for more data while
loading a transmit
queue
Unloading transmit
frame from Synchro-
nous Queue
Unloading transmit
frame from Asynchro-
nous Queue 0
Unloading transmit
frame from Asynchro-
nous Queue 1
Reserved
Current transmit frame
Underrun
Current transmit
queue full.
Current transmit
queue almost full
P R E L I M I N A R Y
SUPERNET 3
this state does not exist in SUPERNET 2, it is added in
SUPERNET 3.
E. QCTRL[2:0] = 111
This state means the number of free long words
remaining in the transmit queue which the current write
request is for has decreased to the almost-full value
(AFULL3-0) programmed in mode register 2. This signal
condition is asserted for one BMCLK cycle only as in the
FORMAC PLUS if the MENAFULL bit in the mode
register 3 is not set. If this bit is set, this state will remain
for every cycle as long as the queue is in almost full
condition and it is not yet full.
Note: If AFULL3-0 is set to 000, this state is not pre-
sented, even when the transmit FIFO in buffer memory
is full.
RDATA1
Receive Data for Receive Queue #1
(TTL output, high impedance)
This signal indicates that received data is present in the
buffer memory and is ready to be transferred by the host
to system memory. Read requests are not acknowl-
edged when RDATA1 is inactive.
RDATA2
Receive Data for Receive Queue #2
(TTL output, high impedance)
This signal indicates that received data is present in the
buffer memory and is ready to be transferred by the host
to system memory. Read requests are not acknowl-
edged when RDATA2 is inactive.
Special Functions and Control Pins
(16 Pins)
FLXI
Flush/Inhibit (TTL input)
The SUPERNET 3 FLXI pin can be programmed to
perform either of two functions: it can provide a flush
received frame function for the chip or it can provide an
unconditional transmit-inhibit function.
If the FLUSH function is selected and the pin is asserted
by external logic, then the incoming frame is flushed.
The buffer memory pointers are not advanced from
where they were before the frame was received. This
prevents unwanted frames and fragments from occupy-
ing receive buffer space and taking up the buffer
memory bus bandwidth.
If the TRANSMIT INHIBIT function is selected and the
pin is asserted by external logic, then the SUPERNET 3
completes transmitting the current frame (if transmit-
ting) releases the token and no further transmissions
can occur until the pin is deasserted. During the time
that the TRANSMIT INHIBIT function is enabled, the
network timers and state machines operate normally.