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Cortina Systems LXT9785 and LXT9785E Advanced 8-Port 10/100 Mbps PHY Transceivers
LXT9785/LXT9785E
Datasheet
249241, Revision 11.0
16 April 2007
4.13 Cable Diagnostics
Overview
4.12.7
Boundary Scan Register
Each Boundary Scan Register (BSR) cell has two stages. A flip-flop and a latch are used
for the serial shift stage and the parallel output stage. There are four modes of operation
as listed in
Table 49. Refer to the Identification Information section in the
Cortina Systems LXT9785 and LXT9785E Advanced 8-Port 10/100 Mbps PHY
Transceivers Specification Update (document number 249357) for the JTAG ID numbers.
4.13
Cable Diagnostics Overview
Debugging cable problems increases the overall cost of owning and operating a local area
network. Cable Diagnostic tools were incorporated into the LXT9785/LXT9785E device to
help customers debug network cable problems. The Cable Diagnostic tools provide the
ability to detect severe cable problems, such as open and short circuits, and determine
the distance to the discontinuity.
4.13.1
Features
The following are three cases to consider for Cable Diagnostics:
Distance to a short circuit between wires of a single twisted-pair
An open circuit
Detection of an improperly terminated cable by the link partner.
An improperly terminated cable will not meet IEEE 802.3 return loss requirements.
Register 29 has been added to control cable testing and report cable testing results.
Cable Diagnostics provides a method to determine the distance to opens and shorts when
the link partner is inactive on the twisted-pair under test. The cable tests produce
undefined results if the link partner is transmitting signals. Implementation methods may
vary depending upon the system use requirements of Cable Diagnostics.
Table 49
BSR Mode of Operation
Mode
Description
1
Capture
2Shift
3
Update
4
System Function
Table 50
Supported JTAG Instructions
Name
Code
Description
Data Register
EXTEST
0000 Hex
External Test
BSR
IDCODE
FFFE Hex
ID Code Inspection
ID REG
SAMPLE
FFF8 Hex
Sample Boundary
BSR
High Z
FFCF Hex
Force Float
Bypass
Clamp
FFEF Hex
Clamp
BSR
BYPASS
FFFF Hex
Bypass Scan
Bypass