XRT74L73 Datasheet, PDF (77/488 Pages) Exar Corporation – 3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER

PRELIMINARY
XRT74L73
3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER
REV. P1.0.1
BIT NUMBER
NAME
6
Multi-PHY Polling Enable
5
Back-to-Back Polling
Enable
4
Direct Status Indication
Enable
TYPE
R/W
R/W
R/W
DESCRIPTION
Multi-PHY Polling Enable:
This READ/WRITE bit-field permits the user to either enable or
disable Multi-PHY Polling for the Transmit UTOPIA Interface
block. If the user implements this feature (and configures the
XRT74L73 device to operate in the Multi-PHY Mode) then the
TxUClav output pin will be driven (either "high" or "low") based
upon the fill-status of the Transmit FIFO within the Channel that
corresponds to the "Transmit UTOPIA Address" that is currently
being applied to the "TxUAddr[4:0]" input pins.
If the user does not implement this feature (and then configures
the XRT74L73 device to operate in the Single-PHY Mode), then
the "TxUClav" output pin will unconditionally reflect the "Transmit
FIFO fill-status" for Channel 0. No attention will be paid to the
address values placed upon the "TxUAddr[4:0]" input pins.
0 - Configures the Transmit UTOPIA Interface block to operate in
the Single-PHY Mode.
1 - Configures the Transmit UTOPIA Interface block to operate in
the Multi-PHY Mode.
Back-to-Back Polling Enable:
This READ/WRITE bit-field permits the user to configure the
Transmit UTOPIA Interface block to support "Back-to-Back Poll-
ing".
Ordinarily, for Multi-PHY polling, the user is required to interleave
all UTOPIA Address values (that are to be placed on the "TxU-
Addr[4:0]" input pins) with the NULL Address (e.g., 0x1F). How-
ever, if the user configures the Transmit UTOPIA Interface block
to operate in the "UTOPIA Level 3" Mode, and if the user also
enables "Back-to-Back Polling", then he/she does not need inter-
leave the UTOPIA Addresses with the NULL Address. In this
case, the user can simply apply a "back-to-back" stream of "rele-
vant" UTOPIA Addresses to the "TxUAddr[4:0]" input pins, and
the XRT74L73 device will respond by driving the TxUClav output
pins to the appropriate states (depending upon the Transmit
FIFO fill-status).
0 - Disables "Back-to-Back" Polling. In this mode, the user must
interleave all UTOPIA Addresses (that are to be applied to the
"TxUAddr[4:0]" input pins) with the NULL Address.
1 - Enables "Back-to-Back" Polling. In this mode, the user does
not need to interleave all UTOPIA Addresses (that are to be
applied to the "TxUAddr[4:0]" input pins) with the NULL Address.
NOTE: In order to configure the Transmit UTOPIA Interface block
to operate in the "Back-to-Back Polling" Mode, the user must
also do the following.
a. Configure the Transmit UTOPIA Interface to operate in the
"UTOPIA Level 3" Mode. This is accomplished by setting
Bit 7 (UTOPIA Level 3 Disable) within this Register to "0".
b. Configure the Transmit UTOPIA Interface to support
"Multi-PHY" Polling. This is accomplished by setting Bit 6
(Multi-PHY Polling Enable) within this register to "1".
78