XRT79L71_1 Datasheet, PDF (50/434 Pages) Exar Corporation – 1-CHANNEL DS3/E3 ATM UNI/PPP/CLEAR-CHANNEL FRAMER IC -

XRT79L71
1-CHANNEL DS3/E3 ATM UNI/PPP/CLEAR-CHANNEL FRAMER IC - REGISTER/MAP DESCRIPTION
REV. 1.0.0
BIT NUMBER
NAME
5
Back-to-Back Polling
Enable
4
3-2
Direct Status Indication
Enable
Receive UTOPIA 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
Receive 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 RxU-
Addr[4:0] input pins) with the NULL Address (e.g., 0x1F). How-
ever, if the user configures the Receive UTOPIA Interface block
to operate in the UTOPIA Level 3 Mode, and if the user also
enables Back-to-Back Polling, then the user 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 RxUAddr[4:0] input pins, and the
XRT79L71 will respond by driving the RxUClav output pins to the
appropriate states (depending upon the Receive FIFO fill-sta-
tus).
0 - Disables Back-to-Back Polling. In this mode, the user must
interleave all UTOPIA Addresses (that are to be applied to the
RxUAddr[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 RxUAddr[4:0] input pins) with the NULL Address.
NOTE: In order to configure the Receive UTOPIA Interface block
to operate in the Back-to-Back Polling Mode, the user
must also do the following.
a. Configure the Receive 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 Receive 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 Receive UTOPIA Data Bus Width[1:0]:
These READ/WRITE bit-fields permit the user to select the width
of the Receive UTOPIA Interface Data Buses. The relationship
between the contents of these bit-fields and the corresponding
widths of the Receive UTOPIA Interface Data Bus is tabulated
below.
Receive UTOPIA
Data Bus
Width[1:0]
0
0
0
1
1
0
1
1
Corresponding
Receive UTOPIA
Data Bus Width
Not Valid
8 bits
16 bits
Not Valid
41