DP83849CVSSLASHNOPB datasheet(71/100 Pages) TI2

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7.3 Link Diagnostics Registers - Page 2

Page 2 Link Diagnostics Registers are accessible by setting bits [1:0] = 10 of PAGESEL (13h).

7.3.1

100Mb Length Detect Register (LEN100_DET), Page 2, address 14h

This register contains linked cable length estimation in 100Mb operation. The cable length is an estimation of the effec-

tive cable length based on the characteristics of the recovered signal. The cable length is valid only during 100Mb oper-

ation with a valid Link status indication.

7.3.2

100Mb Frequency Offset Indication Register (FREQ100), Page 2, address 15h

This register returns an indication of clock frequency offset relative to the link partner. Two values can be read, the long

term Frequency Offset, or a short term Frequency Control value. The Frequency Control value includes short term

phase correction. The variance between the Frequency Control value and the Frequency Offset can be used as an indi-

cation of the amount of jitter in the system

Table 43. 100Mb Length Detect Register (

LEN100_DET), address 14h

Bit

Bit Name

Default

Description

15:8

RESERVED

0, RO

RESERVED: Writes ignored, read as 0.

7:0

CABLE_LEN

0, RO

Cable Length Estimate:

Indicates an estimate of effective cable length in meters. A value

of FF indicates cable length cannot be determined.

Table 44. 100Mb Frequency Offset Indication Register (FREQ100), address 15h

Bit

Bit Name

Default

Description

SAMPLE_FREQ

0, RW

Sample Frequency Offset:

If Sel_FC is set to a 0, then setting this bit to a 1 will poll the DSP

for the long-term Frequency Offset value. The value will be avail-

able in the Freq_Offset bits of this register.

If Sel_FC is set to a 1, then setting this bit to a 1 will poll the DSP

for the current Frequency Control value. The value will be available

in the Freq_Offset bits of this register.

This register bit will always read back as 0.

14:9

RESERVED

0, RO

RESERVED: Writes ignored, read as 0.

SEL_FC

0, RW

Select Frequency Control:

Setting this bit to a 1 will select the current Frequency Control value

instead of the Frequency Offset. This value contains Frequency

Offset plus the short term phase correction and can be used to in-

dicate amount of jitter in the system. The value will be available in

the Freq_Offset bits of this register.

7:0

FREQ_OFFSET

0, RO

Frequency Offset:

Frequency offset value loaded from the DSP following assertion of

the Sample_Freq control bit. The Frequency Offset or Frequency

Control value is a twos-complement signed value in units of ap-

proximately 5.1562ppm. The range is as follows:

0x7F = +655ppm

0x00 = 0ppm

0x80 = -660ppm

DP83849CVS/NOPB Datasheet(PDF) 71 Page - Texas Instruments

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