XRT73L04A
4 CHANNEL DS3/E3/STS-1 LINE INTERFACE UNIT
REV. 2.0.3
57
This bit-field has no defined functionality
Command Register CR4-(n)
The bit-format and default values for Command Reg-
ister CR4 are listed below followed by the function of
each of these bit-fields.
Bit D4 - Reserved
This bit-field has no defined functionality
Bit D3 - STS-1/(DS3_(n)) - Channel(n) - Mode Se-
lect
This Read/Write bit field is used to configure Chan-
nel(n) to operate in either the SONET STS-1 Mode or
the DS3 Mode.
Writing a "0" into this bit-field configures Channel(n)
to operate in the DS3 Mode. Writing a "1" into this
bit-field configures Channel(n) to operate in the SO-
NET STS-1 Mode.
N
OTE
: This bit-field is ignored if the E3_(n) bit-field (e.g.,
D2 within this Command Register) is set to "1".
Bit D2 - E3 Mode Select - Channel(n)
This Read/Write bit-field is used to configure Chan-
nel(n) to operate in the E3 Mode.
Writing a "0" into this bit-field configures Channel(n)
to operate in either the DS3 or SONET STS-1 Mode
as specified by the setting of the DS3 bit-field within
this Command Register. Writing a "1" into this bit-
field configures Channel(n) to operate in the E3
Mode.
Bit D1 - LLB_(n) (Local Loop-Back - Channel(n))
This Read/Write bit-field along with RLB_(n) is used
to configure Channel(n) to operate in any one of a va-
riety of Loop-Back modes.
Table 8 relates the contents of LLB_(n) and RLB_(n)
and the corresponding Loop-Back mode for Chan-
nel(n).
Bit D0 - RLB_(n) (Remote Loop-Back - Chan-
nel(n))
This Read/Write bit-field, along with LLB_(n), is used
to configure Channel(n) to operate in any one of a va-
riety of Loop-Back modes.
Table 8 relates the contents of LLB_(n) and RLB_(n)
and the corresponding Loop-Back mode for Chan-
nel(n).
5.3
O
PERATING
THE
M
ICROPROCESSOR
S
ERIAL
I
NTERFACE
.
The XRT73L04A Serial Interface is a simple four wire
interface that is compatible with many of the micro-
controllers available in the market. This interface
consists of the following signals:
• CS - Chip Select (Active Low)
• SClk - Serial Clock
• SDI - Serial Data Input
• SDO - Serial Data Output
Using the Microprocessor Serial Interface
The following instructions for using the Microproces-
sor Serial Interface are best understood by referring
to the diagram in Figure 38 and the timing diagram in
Figure 39.
In order to use the Microprocessor Serial Interface, a
clock signal must be first applied to the SClk input pin.
Then, initiate a Read or Write operation by asserting
the active-low Chip Select input pin CS. It is impor-
tant to assert the CS pin (e.g., toggle it “Low") at least
5ns prior to the very first rising edge of the clock sig-
nal.
Once the CS input pin has been asserted, the type of
operation and the target register address must now
be specified. Provide this information to the Micro-
processor Serial Interface by writing eight serial bits
of data into the SDI input.
COMMAND REGISTER CR4-(n)
D4
D3
D2
D1
D0
Reserved STS-1/DS3_(n)
E3_(n)
LLB_(n) RLB_(n)
0
0
0
0
0
T
ABLE
8: C
ONTENTS
OF
LLB_(n)
AND
RLB_(n)
AND
THE
C
ORRESPONDING
L
OOP
-B
ACK
M
ODE
FOR
C
HANNEL
(n)
LLB
_(n)
RLB
_(n)
L
OOP
-B
ACK
M
ODE
(
FOR
C
HANNEL
(n)
)
0
0
None
1
0
Analog Loop-Back Mode (See Section 4.1 for details)
1
1
Digital Loop-Back Mode (See Section 4.2 for details)
0
1
Remote Loop-Back Mode (See Section 4.3 for details)
