XRT73LC00 Datasheet, PDF (24/53 Pages) Exar Corporation – E3/DS3/STS-1 LINE INTERFACE UNIT

XRT73LC00
E3/DS3/STS-1 LINE INTERFACE UNIT
REV. P1.0.1
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PRELIMINARY
The HOST Mode
To configure the XRT73LC00 to operate in the HOST
Mode, connect the HOST/HW input pin (pin 18) to
VDD.
When the XRT73LC00 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 XRT73LC00 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 SELECTING THE DATA RATE
The XRT73LC00 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 XRT73LC00 is operat-
ing in the Hardware or HOST Mode.
TABLE 2: SELECTING THE DATA RATE FOR THE XRT73LC00 VIA THE E3 AND STS-1/DS3 INPUT PINS (HARDWARE
MODE)
DATA RATE
STATE OF E3 PIN
(PIN 17)
STATE OF STS-1/DS3 PIN
(PIN 16)
MODE OF B3ZS/HDB3 ENCODER/
DECODER BLOCKS
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
A. When operating in the Hardware Mode.
To configure the XRT73LC00 for the desired data
rate, the E3 and the STS-1/DS3 pins must be set to
the appropriate logic states shown in Table 2.
B. When operating in the HOST Mode.
To configure the XRT73LC00 for the desired data
rate, appropriate values need to be written into the
STS-1/DS3 and E3 bit-fields in Command Register
CR4.
COMMAND REGISTER CR4 (ADDRESS = 0X04)
D4
D3
D2
D1
D0
X
STS-1/DS3 E3
LLB
RLB
X
X
X
X
X
Table 3 relates the values of these two bit-fields with
respect to the selected data rates.
TABLE 3: SELECTING THE DATA RATE FOR THE
XRT73LC00 VIA THE STS-1/DS3 AND THE E3 BIT-
FIELDS WITHIN COMMAND REGISTER CR4 (HOST
MODE)
SELECTED DATA RATE
STS-1/DS3
E3
E3
Don't Care
1
DS3
0
0
STS-1
1
0
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.
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