XRT79L71 Datasheet, PDF (105/441 Pages) Exar Corporation – 1 - CHANNEL DS3/E3 ATM UNI/PPP COMBO IC

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PRELIMINARY
1 - CHANNEL DS3/E3 ATM UNI/PPP COMBO IC
XRT79L71
REV. P1.0.3
BIT NUMBER
NAME
5
Back-to-Back Polling
Enable
4
Direct Status Indication
Enable
3-2
UTOPIA/POS-PHY Data
Bus Width[1:0]
TYPE
R/W
R/W
DESCRIPTION
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 XRT79L71 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".
R/W
UTOPIA/POS-PHY Data Bus Width[1:0]:
These READ/WRITE bit-fields permit the user to select the width
of the Transmit UTOPIA and POS-PHY Data Buses. The rela-
tionship between the contents of these bit-fields and the corre-
sponding widths of the Transmit UTOPIA and POS-PHY Data
Bus is tabulated below.
UTOPIA/PO S-PHY
Data Bus
W idth[1:0]
0
0
0
1
1
0
1
1
C o rre s p o n d in g
UTOPIA/PO S-PHY
Data Bus W idth
Not Valid
8 bits
16 bits
Not Valid
93