
XRT73L00
E3/DS3/STS-1 LINE INTERFACE UNIT
REV. 1.2.0
á
21
The HOST Mode
To configure the XRT73L00 to operate in the HOST
Mode, connect the HOST/HW input pin (pin 18) to
VDD.
When the XRT73L00 is operating in the HOST Mode,
the following is true:
1.
The Microprocessor Serial Interface block is
enabled. Many configuration selections are
made by writing the appropriate data into the on-
chip Command Registers via the Microprocessor
Serial Interface.
2.
All of the following input pins are disabled:
Pin 1 - TXLEV
Pin 2 - TAOS
Pin 12 - REQDIS
Pin 14 - LLB
Pin 15 - RLB
Pin 16 - STS-1/DS3
Pin 17 - E3
Pin 35 - TXOFF
Tie each of these pins to GND if the XRT73L00 IC is
to be operated in the HOST Mode.
Please see Section 5.0 for a detailed description on
operating the Microprocessor Serial Interface or the
on-chip Command Registers.
1.0
The XRT73L00 can be configured to support the E3
(34.368 Mbps), DS3 (44.736 Mbps) or the SONET
STS-1 (51.84 Mbps) rates. Selection of the data rate
is dependent on whether the XRT73L00 is operating
in the Hardware or HOST Mode.
SELECTING THE DATA RATE
A. When operating in the Hardware Mode.
To configure the XRT73L00 for the desired data rate,
the E3 and the STS-1/DS3 pins must be set to the ap-
propriate logic states shown in Table 2.
B. When operating in the HOST Mode.
To configure the XRT73L00 for the desired data rate,
appropriate values need to be written into the STS-1/
DS3 and E3 bit-fields in Command Register CR4.
Table 3 relates the values of these two bit-fields with
respect to the selected data rates.
The results of making these selections are:
1.
The VCO Center Frequency of the Clock Recov-
ery Phase-Locked-Loop is configured to match
the selected data rate.
2.
The B3ZS/HDB3 Encoder and Decoder blocks
are configured to support B3ZS Encoding/Decod-
ing if the DS3 or STS-1 data rates were selected
or,
3.
The B3ZS/HDB3 Encoder and Decoder blocks
are configured to support HDB3 Encoding/
Decoding if the E3 data rate was selected.
T
ABLE
2: S
ELECTING
THE
D
ATA
R
ATE
FOR
THE
XRT73L00
VIA
THE
E3
AND
STS-1/DS3
INPUT
PINS
(H
ARDWARE
M
ODE
)
D
ATA
R
ATE
S
TATE
OF
E3 P
IN
(P
IN
17)
S
TATE
OF
STS-1/DS3
PIN
(P
IN
16)
M
ODE
OF
B3ZS/HDB3 E
NCODER
/
D
ECODER
B
LOCKS
E3 (34.368 Mbps)
VDD
X (Don’t Care)
HDB3
DS3 (44.736 Mbps)
0
0
B3ZS
STS-1 (51.84 Mbps)
0
VDD
B3ZS
COMMAND REGISTER CR4 (ADDRESS = 0X04)
D4
D3
D2
D1
D0
X
STS-1/DS3
E3
LLB
RLB
X
X
X
X
X
T
ABLE
3: S
ELECTING
THE
D
ATA
R
ATE
FOR
THE
XRT73L00 V
IA
THE
STS-1/DS3
AND
THE
E3 B
IT
-
FIELDS
W
ITHIN
C
OMMAND
R
EGISTER
CR4 (HOST
M
ODE
)
S
ELECTED
D
ATA
R
ATE
STS-1/DS3
E3
E3
Don't Care
1
DS3
0
0
STS-1
1
0