XRT74L73
3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER
REV. P1.0.1
PRELIMINARY
229
Table 49 relates the content of this bit-field to the Bi-
polar Line Code that DS3 Data will be transmitted
and received at.
N
OTES
:
1. This bit is ignored if the Unipolar mode is selected.
2. This selection also effects the operation of the
Receive DS3 LIU Interface block
4.2.5.2
TxLineClk Clock Edge Selection
The Framer also allows the user to specify whether
the DS3 output data (via TxPOS and/or TxNEG out-
put pins) is to be updated on the rising or falling edg-
es of the TxLineClk signal. The purpose of this fea-
ture is to insure that the Framer will always be able to
output data to the LIU IC, in such a way that the LIU
set-up and hold time requirements can always be
met. This selection is made by writing to bit 2 of the I/
O Control Register, as depicted below.
Table 50 relates the contents of this bit field to the
clock edge of TxClk that DS3 Data is output on the
TxPOS and/or TxNEG output pins.
I/O CONTROL REGISTER (ADDRESS = 0X01)
B
IT
7
B
IT
6
B
IT
5
B
IT
4
B
IT
3
B
IT
2
B
IT
1
B
IT
0
Disable
TxLOC
LOC
Disable
RxLOC
AMI/ZeroSup*
Unipolar/
Bipolar*
TxLine CLK
Invert
RxLine CLK
Invert
Reframe
R/W
RO
R/W
R/W
R/W
R/W
R/W
R/W
1
0
1
0
0
0
0
0
T
ABLE
49: T
HE
R
ELATIONSHIP
BETWEEN
B
IT
4 (AMI/B3ZS*)
WITHIN
THE
I/O C
ONTROL
R
EGISTER
AND
THE
B
IPOLAR
L
INE
C
ODE
THAT
IS
OUTPUT
BY
THE
T
RANSMIT
DS3 LIU I
NTERFACE
B
LOCK
B
IT
4
B
IPOLAR
L
INE
C
ODE
0
B3ZS
1
AMI
II/O CONTROL REGISTER (ADDRESS = 0X01)
B
IT
7
B
IT
6
B
IT
5
B
IT
4
B
IT
3
B
IT
2
B
IT
1
B
IT
0
Disable
TxLOC
LOC
Disable
RxLOC
AMI/ZeroSup*
Unipolar/
Bipolar*
TxLine CLK
Invert
RxLine CLK
Invert
Reframe
R/W
RO
R/W
R/W
R/W
R/W
R/W
R/W
1
0
1
0
0
X
X
0
T
ABLE
50: T
HE
R
ELATIONSHIP
BETWEEN
THE
CONTENTS
OF
B
IT
2 (T
X
L
INE
C
LK
I
NV
)
WITHIN
THE
I/O C
ONTROL
R
EGISTER
AND
THE
T
X
L
INE
C
LK
CLOCK
EDGE
THAT
T
X
POS
AND
T
X
NEG
ARE
UPDATED
ON
B
IT
2
R
ESULT
0
Rising Edge:
Outputs on TxPOS and/or TxNEG are updated on the rising edge of TxLineClk.
See Figure 77 for timing relationship between TxLineClk, TxPOS and TxNEG signals, for this selection.
1
Falling Edge:
Outputs on TxPOS and/or TxNEG are updated on the falling edge of TxLineClk.
See Figure 78 for timing relationship between TxLineClk, TxPOS and TxNEG signals, for this selection.