GS6151 datasheet(40/77 Pages) SEMTECH

40 / 77 page

GS6151

Final Data Sheet

Rev.4

PDS-060389

August 2015

40 of 77

Semtech

Proprietary & Confidential

www.semtech.com

4.12 Diagnostic Features

To aid in debug, the GS6151 has an on-chip eye monitoring, error counting and

PRBS-signal generation features that can be used to check system links for error-free

operation. The PRBS signal generator outputs a PRBS7 bit stream (x7+x6+1 polynomial)

or clock (at the reference or divided rates) which can be clocked from either an on-chip

or off-chip source. The eye monitor is a 128-bit horizontal eye monitor (HEM) that can

automatically detect the error-free eye width, the first error-free phase position and

provide a bitmap of the error status of each phase without affecting the retiming

capability of the CDR. Additionally, the HEM can be configured to manually count the

number of errors at a given phase for a given time interval or to continually count errors

until programmed to stop. In any of these three modes, described in the next section,

Section 4.12.1, the criteria for measuring a bit error can also be set to measure bit errors

of arbitrary data (in which the input to the CDR is assumed to be BER-free at some phase)

or by checking against a PRBS7 bit stream for measuring error-free performance of

upstream devices. PRBS checking is described in Section 4.12.2. The PRBS generator is

described in Section 4.12.3. The HEM and PRBSCHK features operate at 3Gb/s and HD

data rates, while the PRBS generator operates at 3G, HD, SD and MADI rates.

4.12.1 Horizontal Eye Monitor Modes

The three modes of bit error characterization of the HEM are described below. In this

section it is assumed that arbitrary data is being input and checked. For each of these

modes (and the PRBS7 input data checking mode in section 4.12.3) the Horizontal Eye

Monitor must be enabled by setting the HORIZONTAL_EYE_MON_ENABLE bit of the

EYE_MON_ENABLE register at address 23h.

4.12.1.1 Automatic Eye Scan

The automatic eye-scan mode measures the error-free eye width and first error-free

phase (EYE_WIDTH and STARTING_PHASE bits, respectively, of

EYE_MON_STATUS_REG_2) position as well as the resultant error bitmap of each of the

128 phases (EYE_BITMAP bits of EYE_MON_STATUS_REG_4 to

EYE_MON_STATUS_REG_11, least-significant bits correspond to leftmost bits). A bit

value of 1 in the bitmap indicates error-free operation at the phase that corresponds to

the bit. A bit value of 0 indicates more than the ERROR_THRESHOLD number of errors

have been counted and the bit is considered as an error bit. It should be noted that the

eye is not necessarily centered in the results, i.e. the crossing may be in the center of the

bitmap and the open eye can wrap around from phase 127 back to 0. The automatic eye

scan takes this into account and calculates the value for the error-free eye across the

wrapping while the error-free phase corresponds to the leftmost portion of the

error-free eye rather than the leftmost error-free phase in the bitmap. Refer to

Figure 4-22 below.

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