XRT72L50 Datasheet, PDF (296/471 Pages) Exar Corporation – SINGLE CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER

XRT72L50
SINGLE CHANNEL DS3/E3 FRAMER WITH HDLC CONTROLLER
REV. 1.2.1
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The Transmit E3 LIU Interface block can transmit data to the LIU IC or other external circuitry via two different
output modes: Unipolar or Bipolar. If the user selects Unipolar (or Single Rail) mode, then the contents of the
E3 Frame is output, in a binary (NRZ manner) data stream via the TxPOS pin to the LIU IC. The TxNEG pin
will only be used to denote the frame boundaries. TxNEG will pulse "High" for one bit period, at the start of
each new E3 frame, and will remain "Low" for the remainder of the frame. Figure 110 presents an illustration of
the TxPOS and TxNEG signals during data transmission while the Transmit E3 LIU Interface block is operating
in the Unipolar mode. This mode is sometimes referred to as Single Rail mode because the data pulses only
exist in one polarity: positive.
FIGURE 110. THE BEHAVIOR OF TXPOS AND TXNEG SIGNALS DURING DATA TRANSMISSION WHILE THE TRANSMIT
E3 LIU INTERFACE IS OPERATING IN THE UNIPOLAR MODE
Data _{1 0 1 1 0 0 1 0 0 1 1 1 0 1 0 1 0 0 1}
TxPOS
1 10
01
TxNEG
TxLineClk
Frame Boundary
When the Transmit E3 LIU Interface block is operating in the Bipolar (or Dual Rail) mode, then the contents of
the E3 Frame is output via both the TxPOS and TxNEG pins. If the Bipolar mode is chosen, then E3 data can
be transmitted to the LIU via one of two different line codes: Alternate Mark Inversion (AMI) or High Density
Bipolar -3 (HDB3). Each one of these line codes will be discussed below. Bipolar mode is sometimes referred
to as Dual Rail because the data pulses occur in two polarities: positive and negative. The role of the TxPOS,
TxNEG and TxLineClk output pins, for this mode are discussed below.
TxPOS - Transmit Positive Polarity Pulse: The Transmit E3 LIU Interface block will assert this output to the
LIU IC when it desires for the LIU to generate and transmit a positive polarity pulse to the remote terminal
equipment.
TxNEG - Transmit Negative Polarity Pulse: The Transmit E3 LIU Interface block will assert this output to the
LIU IC when it desires for the LIU to generate and transmit a negative polarity pulse to the remote terminal
equipment.
TxLineClk - Transmit Line Clock: The LIU IC uses this signal from the Transmit E3 LIU Interface block to
sample the state of its TxPOS and TxNEG inputs. The results of this sampling dictates the type of pulse
(positive polarity, zero, or negative polarity) that it will generate and transmit to the remote Receive E3 Framer.
5.2.5.1 Selecting the various Line Codes
The user can select either the Unipolar Mode or Bipolar Mode by writing the appropriate value to Bit 3 of the I/
O Control Register (Address = 0x01), as shown below.
I/O Control Register (Address = 0x01)
BIT 7
Disable TxLOC
BIT 6
LOC
R/W
RO
1
0
BIT 5
Disable
RxLOC
R/W
1
BIT 4
AMI/ZeroSup
R/W
0
BIT 3
Unipolar/
Bipolar
R/W
0
BIT2
BIT 1
TxLine CLK RxLine CLK
Invert
Invert
R/W
R/W
0
0
Table 53 relates the value of this bit field to the Transmit E3 LIU Interface Output Mode.
BIT 0
Reframe
R/W
0
283