![](http://datasheet.mmic.net.cn/Exar-Corporation/XRT94L33IB-L_datasheet_100163/XRT94L33IB-L_168.png)
XRT94L33
xr
Rev.1.2.0.
3-CHANNEL DS3/E3/STS-1 TO STS-3/STM-1 MAPPER IC DATA SHEET
168
output signal “l(fā)ow” if its TxFIFO is too full and is incapable of receiving one more complete cell of data from
the ATM Layer processor.
When UNI #2 has been selected for “polling”, UNI #1 will continue to keeps its “TxUClav” output signal “tri-
stated”. Therefore, when UNI #2 is driving its “TxUClav” output pin to the appropriate level; it will be driving
the entire “TxUClav” line, within the “Multi-PHY” system.
Consequently, UNI#2 will also be driving the
“TxUClav_in” input pin of the ATM Layer processor (see Figure 26).
If UNI #2 drives the “TxUClav” line “l(fā)ow”, upon the application of its address on the UTOPIA Address Bus,
then the ATM Layer processor will “l(fā)earn” that it cannot write any more cell data to this UNI device; and will
deem this device “unavailable”. However, if UNI #2 drives the TxUClav line “high” (during “polling”), then the
ATM Layer processor will know that it can write more ATM cell data into the Transmit UTOPIA Interface block,
of UNI # 2.
Figure 16 presents a timing diagram, that depicts the behavior of the ATM Layer processor’s and the UNI’s
Figure 16:Timing Diagram illustrating the Behavior of various signals from the ATM Layer processor
and the UNI, during Polling
TxUClk
TxUAddr[4:0]
TxUClav
TxUEnB*
TxUData[15:0]
TxUSoC
0x00
1Fh
0x02
0x1F
0x00
0x02
0x1F
0x02
0x00
0x1F
0x00
0x02
W27
W0
W1
W2
W3
W4
W5
W6
W7
W8
W9
W10
0x00
0x02
0x00
0x02
0x00
1
2
3
4
5
6
7
8
9
10
11
12
1. The Transmit UTOPIA Data Bus is configured to be 16 bits wide. Hence, the data, which the ATM Layer
processor places on the Transmit UTOPIA Data bus, is expressed in terms of 16-bit words: (e.g., W0 - W26.)
2. The Transmit UTOPIA Interface Block is configured to handle 54 bytes/cell. Hence, Figure 27 illustrates
the ATM Layer processor writing 27 words (W0 through W26) for each ATM cell.
3. The ATM Layer processor is currently writing ATM cell data to the Transmit UTOPIA Interface Block, within
UNI #1 (TxUAddr[4:0] = 0x00) during this “polling process”.
4.
The TxFIFO, within UNI#2’s Transmit UTOPIA Interface block (TxUAddr[4:0] = 0x02) is incapable of
receiving any additional ATM cell data from the ATM Layer processor. Hence, the TxUClav line will be driven
“l(fā)ow” whenever this particular Transmit UTOPIA Interface block is “polled”.
5. The Transmit UTOPIA Address of 0x1F (e.g., the NULL address), is not associated with any UNI device,
within this “Multi-PHY” system. Hence, the TxUClav line is tri-stated whenever this address is “polled”.
Note:
Although Figure 26 depicts connections between the Receive UTOPIA Interface block pins and the ATM Layer
processor; the Receive UTOPIA Interface block operation, in the Multi-PHY mode, will not be discussed in this
section.
Please see Section _ for a discussion on the Receive UTOPIA Interface block during Multi-PHY
operation.
2.2.1.3.10
ATM Layer Processor “polling” with the XRT94L33
In
Figure 15, a simple illustration of the “Conceptual Multi-PHY” system consisting of two single-channel UNI
devices was presented. In reality, a given Multi-PHY system can or will consist of numerous “multi-channel”
UNI devices.
The XRT94L33 is an example of this, being a “4-channel” UNI device.
Therefore, the