Micrel, Inc.
SY87725L Evaluation Board
July 2008
9
M9999-071108-B
hbwhelp@micrel.com
or (408) 955-1690
Local Loopback Data Flow
Verifies correct operation of the transmit 4-bit Mux and
the receive 4-bit DeMux through the parallel interface. In
this mode parallel clock and data are applied to the
CLKIN and DIN0-3 transmit inputs and is then serialized
and fed into the receive 4-bit DeMux where it is output at
the CLKOUT and 4-bit parallel DOUT0-3 outputs. The
CLKIN is multiplied by 4 up to the serial rate by the
synthesizer (clock multiplier). This allows a parallel BERT
to be used to verify the Mux and DeMux operation
independent of the CDR.
Figure 5. Switch Settings for Local Loopback Data
Switch Settings
Function
RCV_DDRSEL = 0
Sets Clkout to be at parallel data
rate
RCV_CTRL0/1 = 10 Sets up local loopback
XMT_FSEL0/1 = 01 Sets parallel data rate to be
1.24416Gbps/4
TESTb = 1
Disables factory test mode
(enables normal operation)
XMT_DDRSEL = 0
Selects CLKIN to be at parallel
data rate. CLKIN must correspond
to the DIN0-3 data rate.
Table 6. Required Switch Settings for
Local Loopback Data Flow
