32
x r
PRELIMINARY
E3 UNI FOR ATM
XRT7234
REV. P1.0.0
81
123
TxEnB*
I
Transmit Utopia Interface Block—Write Enable:
This active-low signal,
from the ATM Layer processor enables the data on the Transmit Utopia
Data Bus to be written into the TxFIFO on the rising edge of TxClk.
When this signal is asserted, then the contents of the byte or word that is
present, on the Transmit Utopia Data Bus, will be latched into the Transmit
Utopia Interface block, on the rising edge of TxClk.
When this signal is negated, then the Transmit Utopia Data bus inputs
will be tri-stated.
82
124
TxSoC
I
Transmitter—Start of Cell (SoC) Indicator Input:
This input pin is driven
by the ATM Layer processor and is used to indicate the start of an ATM
cell that is being transmitted from the ATM layer device. This input pin
must be pulsed “high” when the first byte (or word) of a new cell is
present on the Transmit Utopia Data Bus. This input pin must remain
“l(fā)ow” at all other times.
83
125
TxPrty
I
Transmit Utopia Data Bus—Parity Input:
The ATM Layer processor
will apply the parity value of the byte or word which is being applied to
the Transmit Utopia Data Bus (e.g., TxData[7:0] or TxData[15:0]) inputs
of the UNI, respectively. Note: this parity value should be computed
based upon the odd-parity of the data applied at the Transmit Data Bus.
The Transmit Utopia Interface block (within the UNI) will independently com-
pute the odd-parity value of each byte (or word) that it receives from the
ATM Layer processor and will compare it with the logic level of this input
pin.
84
126
TxClav
O
Transmit Utopia Interface—Cell Available Output Pin:
This output pin
supports data flow control between the ATM Layer processor and the
Transmit Utopia Interface block. The exact functionality of this pin depends
upon whether the UNI is operating in the “Octet Level” or “Cell Level”
handshaking mode.
Octet Level Handshaking:
When the Transmit Utopia Interface block is
operating in the octet-level handshaking mode, this signal is negated
(toggles “l(fā)ow”) when the TxFIFO is not capable of handling four more
write operations; by the ATM Layer processor to the Transmit Utopia
Interface block. This signal will be asserted when the TxFIFO is capable
of receiving four or more write operation of ATM cell data.
Cell Level Handshaking:
When the Transmit Utopia Interface block is
operating the cell-level handshaking mode, this signal is asserted (toggles
“high”) when the TxFIFO is capable of receiving at least one more full
cell of data from the ATM Layer processor. This signal is negated, if the
TxFIFO is not capable of receiving one more full cell of data from the
ATM Layer processor.
Multi-PHY Operation:
When the UNI chip is operating in the Multi-PHY
mode, this signal will be tri-stated until the TxClk cycle following the
assertion of a valid address on the Transmit Utopia Address bus input
pins (e.g., when the contents on the Transmit Utopia Address bus pins
match that within the Transmit Utopia Address Register). Afterwards, this
output pin will behave in accordance with the cell-level handshake mode.
PIN DESCRIPTION (CONTINUED)
Pin
No.
100 Pin Package
Pin No. 160
PinPackage
Symbol
Type
Description