
XRT7245
DS3 UNI FOR ATM
á
PRELIMINARY
REV. 1.03
282
Final Comments on Single-PHY Mode
The RxClav pin exhibits a role that is similar to the
“Ready Ready” function in RS-232 based data com-
munication. This pin is asserted when the RxFIFO
contains ATM cell data that can be read by the ATM
Layer processor. The RxClav pin will have a slightly
different role when the UNI is operating in the Multi-
PHY mode.
The UNI, while operating in Single-PHY mode, can
be configured for either “Octet-Level” or “Cell Level”
handshake modes. In either case, the ATM Layer
Processor is expected to poll the RxClav pin before
attempting to read in the next byte, word or cell from
the RxFIFO.
7.4.2.2.3.1
The UNI IC will be operating in the Multi-PHY mode
upon power up or reset. In Multi PHY operating
mode, the ATM layer processor may be pumping data
into and reading data from several UNI devices in
parallel. When the UNI is operating in Multi-PHY mode,
the Receive UTOPIA Interface block will support two
kinds of operations with the ATM Layer processor.
Polling for “available” UNI devices.
Selecting which UNI (out of several possible UNI
devices) to read ATM cell data from.
Multi-PHY Operation
Each of these operations are discussed in the sections
below. However, prior to discussing each of these
operations, the reader must understand the following.
“Multi-PHY” operation involves the use of one (1)
ATM Layer processor and several UNI devices, within
a system. The ATM Layer processor is expected to
read/write ATM cell data from/to these UNI devices.
Hence, “Multi-PHY” operation requires, at a minimum,
some means for the ATM Layer processor to uniquely
identify a UNI device (within the “Multi-PHY” system)
that it wishes to “poll”, write ATM cell data to, or read
ATM cell data from. Actually, “Multi-PHY” operation
provides an addressing scheme that allows the ATM
Layer processor to uniquely identify “UTOPIA Interface
Blocks” (e.g., Transmit and Receive) within all of the
UNI devices, operating in the “Multi-PHY” system. In
order to uniquely identify a given “UTOPIA Interface
Block”, within a “Multi-PHY” system, each “UTOPIA
Interface block” is assigned a 5-bit “UTOPIA Address”
value. The user assigns this address value to a par-
ticular “Receive UTOPIA Interface block” by writing
this address value into the “Rx UTOPIA Address
Register” (Address = 6Ch) within its “host” UNI
device. The bit-format of the “Rx UTOPIA Address
Register” is presented below.
Likewise, the user assigns a “UTOPIA address” value
to a particular “Transmit UTOPIA Interface block”,
within one of the UNIs (in the “Multi-PHY” system) by
writing this address value into the “Tx UTOPIA
Address Register” (Address = 70h) within the “host”
UNI device. The bit-format of the “Tx UTOPIA
Address Register” is presented below.
Note:
The role of the Transmit UTOPIA Interface block, in
“Multi-PHY” operation is presented in Section 6.1.2.3.2.
7.4.2.2.3.1.1
ATM Layer Processor “polling” of
the UNIs, in the Multi-PHY Mode
When the UNI is operating in the “Multi-PHY” mode,
the Receive UTOPIA Interface block will automatically
be configured to support “polling”. “Polling” allows an
Receive UTOPIA Address Register: (Address = 6Ch)
B
IT
7
B
IT
6
B
IT
5
B
IT
4
B
IT
3
B
IT
2
B
IT
1
B
IT
0
Unused
Rx_UTOPIA_Addr[4:0]
RO
RO
RO
R/W
R/W
R/W
R/W
R/W
0
0
0
0
0
0
0
0
Tx UTOPIA Address Register (Address = 70h)
B
IT
7
B
IT
6
B
IT
5
B
IT
4
B
IT
3
B
IT
2
B
IT
1
B
IT
0
Unused
Tx_UTOPIA_Addr[4:0]
RO
RO
RO
R/W
R/W
R/W
R/W
R/W
0
0
0
0
0
0
0
0