Micrel, Inc.
SY87725L Evaluation Board
July 2008
7
M9999-071108-B
or (408) 955-1690
Remote Loopback Recovered Data
Verifies correct operation of the receive CDR. A RefClk of
155.52MHz or 77.76MHz (selected by REFFREQSEL)
must be supplied for the CDR to function. When CD is
HIGH, the recovered data coming out of SOUT will be the
same data coming into SIN (retimed). CDR operation can
be verified with a serial BERT.
Figure 3. Switch Settings for Remote Loopback
Recovered Data
Switch Settings
Function
RCV_FSEL0/1 = 11
Sets receive CDR frequency to
2.48832Gbps (For other
frequencies, refer to Receive
Frequency Selection Table on
page 7 of SY87725L Data
sheet.)
TESTb = 1
Disables factory test mode
(enables normal operation)
CD = 1
Enables clock and data recovery
REFFREQSEL = 1
Selects RefClk of 155.52MHz
XMT_CTRL0/1 - 01
Selects the remote loopback
mode so SDOUT = recovered
data
Table 4. Required Switch Settings for
Remote Loopback Recovered Data Flow
