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PRELIMINARY
DS3 UNI FOR ATM
XRT7245
REV. 1.03
285
Figure 93 presents a timing diagram, that depicts the
behavior of the ATM Layer processor’s and the UNI’s
signals during polling.
Note:
regarding Figure 93
1. The Receive UTOPIA Data bus is configured to be
16 bits wide. Hence, the data, which the ATM Layer
processor places on the Receive UTOPIA Data
bus, is expressed in terms of 16 bit words: (e.g.,
W0–W26).
2. The Receive UTOPIA Interface block is configured
to handle 54 bytes/cell. Hence, Figure 93 illustrates
the ATM Layer processor reading 27 words (W0
through W26) for each ATM cell.
3. The ATM Layer processor is currently reading ATM
cell data from the Receive UTOPIA Interface block,
within UNI #1 (RxAddr[4:0] = 01h) during this “polling
process”.
4. The RxFIFO, within UNI#2’s Receive UTOPIA
Interface block (RxAddr[4:0] = 03h) is either
depleted or does not contain enough data to con-
stitute a complete ATM cell. Hence, the RxClav line
will be driven “l(fā)ow” whenever this particular
Receive UTOPIA Interface block is “polled”.
5. The Receive UTOPIA Address of 1Fh is not asso-
ciated with any UNI device, within this “Multi-PHY”
system. Hence, the RxClav line is tri-stated when-
ever this address is “polled”.
Note:
Although Figure 93 depicts connections between
the Transmit UTOPIA Interface block pins and the ATM
Layer processor; the Transmit UTOPIA Interface operation,
in the Multi-PHY mode, will not be discussed in this section.
Please see Section 6.1.2.3.2.1 for a discussion on the Trans-
mit UTOPIA Interface block during Multi-PHY operation.
7.4.2.2.3.1.2
Reading ATM Cell Data from
a Different UNI
After the ATM Layer processor has “polled” each of
the UNI devices within its system, it must now select
a UNI, and begin reading ATM cell data from that
device. The ATM Layer processor makes its selection
and begins the reading process by:
Applying the UTOPIA Address of the “target” UNI
on the “UTOPIA Address Bus”.
Negate the RxEnB* signal. This step causes the
“addressed” UNI to recognize that it has been
selected to transmit the next set of ATM cell data
to the ATM Layer processor.
Assert the RxEnB* signal.
Check and insure that the RxSoC output pin (of
the selected UNI) pulses “high” when the first
byte or word of ATM cell data has been placed on
the Receive UTOPIA Data Bus.
Begin reading the ATM Cell data in a byte-wide
(or word-wide) manner from the Receive UTOPIA
Data bus.
1.
2.
3.
4.
5.
Figure 94 presents a flow-chart that depicts the “UNI
Device Selection and Read” process in Multi-PHY
operation.
F
IGURE
93. T
IMING
D
IAGRAM
ILLUSTRATING
THE
B
EHAVIOR
OF
VARIOUS
SIGNALS
FROM
THE
ATM L
AYER
PROCESSOR
AND
THE
UNI,
DURING
P
OLLING
.
RxClk
RxAddr[4:0]
RxClav
RxEnB*
RxData[15:0]
RxSoC
01h
1Fh
03h
1Fh
01h
03h
1Fh
03h
01h
1Fh
01h
03h
W27
W0
W1
W2
W3
W4
W5
W6
W7
W8
W9
W10
01h
03h
01h
03h
03h
01h
01h
1
2
3
4
5
6
7
8
9
10
11
12