XRT74L74 Datasheet, PDF (242/498 Pages) Exar Corporation – 4 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER

XRT74L74
REV. P1.1.1
4 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER
ADVANCED CONFIDENTIAL
I/O CONTROL REGISTER (ADDRESS = 0X01)
BIT 7
BIT 6
BIT 5
BIT 4
Disable TxLOC
R/W
1
LOC
RO
0
Disable
RxLOC
R/W
1
AMI/ZeroSup*
R/W
0
Table 49 relates the content of this bit-field to the Bi-
polar Line Code that DS3 Data will be transmitted
and received at.
BIT 3
Unipolar/
Bipolar*
R/W
0
BIT2
TxLine CLK
Invert
R/W
0
BIT 1
RxLine CLK
Invert
R/W
0
BIT 0
Reframe
R/W
0
TABLE 49: THE RELATIONSHIP BETWEEN BIT 4 (AMI/B3ZS*) WITHIN THE I/O CONTROL REGISTER AND THE
BIPOLAR LINE CODE THAT IS OUTPUT BY THE TRANSMIT DS3 LIU INTERFACE BLOCK
BIT 4
0
1
BIPOLAR LINE CODE
B3ZS
AMI
NOTES:
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
5.2.5.2 TxLineClk Clock Edge Selection
The Framer also allows the user to specify whether
the DS3 output data (via TxPOS and/or TxNEG out-
II/O CONTROL REGISTER (ADDRESS = 0X01)
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.
BIT 7
BIT 6
BIT 5
BIT 4
Disable TxLOC
R/W
1
LOC
RO
0
Disable
RxLOC
R/W
1
AMI/ZeroSup*
R/W
0
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.
BIT 3
Unipolar/
Bipolar*
R/W
0
BIT2
TxLine CLK
Invert
R/W
X
BIT 1
RxLine CLK
Invert
R/W
X
BIT 0
Reframe
R/W
0
TABLE 50: THE RELATIONSHIP BETWEEN THE CONTENTS OF BIT 2 (TXLINECLK INV) WITHIN THE I/O CONTROL
REGISTER AND THE TXLINECLK CLOCK EDGE THAT TXPOS AND TXNEG ARE UPDATED ON
BIT 2
0
1
RESULT
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.
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.
NOTE: The user will typically make the selection based
upon the set-up and hold time requirements of the Transmit
LIU IC.
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