
XRT72L52
400
TWO CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER
REV. 1.0.3
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 167 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.
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 the 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.
6.2.5.1
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.
FIGURE 167. THE BEHAVIOR OF TXPOS AND TXNEG SIGNALS DURING DATA TRANSMISSION WHILE THE TRANSMIT
E3 LIU INTERFACE IS OPERATING IN THE UNIPOLAR MODE
I/O CONTROL REGISTER (ADDRESS = 0X01)
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT2
BIT 1
BIT 0
Disable
TxLOC
LOC
Disable
RxLOC
AMI/ZeroSup
Unipolar/
Bipolar
TxLine CLK
Invert
RxLine CLK
Invert
Reframe
R/W
RO
R/W
1
0
1
0
TxPOS
TxNEG
TxLineClk
Data
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
Frame Boundary