SCAN25100

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SNLS223C – SEPTEMBER 2006 – REVISED APRIL 2013

LOS DETECTION

LOS is set to HIGH during receiver power up, during hardware reset (via RESETB pin), or during software (via

RESETB MDIO register) reset. LOS requires one K28.5 character and valid line coding for 1 hyperframe in order

to go from HIGH to LOW. After initialization, the LOS is set on the condition shown in the table below. Also, when

the deserializer loses lock, LOS is not automatically set high since the deserializer continues to count LCV’s in

order to determine LOS status according to the CPRI standard.

Table 12. LOS Set Conditions

OPMODE

Condition

LOS

0 (BTS Mode)

16 or more line code violations in a CPRI hyperframe

1

The LOS mechanism affects the ROUT[9:0] and RXCLK outputs of the device under 8-bit mode. Upon power up,

the ROUT[9:0] and RXCLK pins will be static. Once LOS is low, the device will send data on the ROUT[9:0] and

RXCLK pins. After LOS is high, the output will continue to send data for 2-3 hyperframes. If there are no line

code violations during the next hyperframe, the LOS signal goes low and resumes normal operation. If there are

line code violations after the next 2-3 hyperframes, the outputs will be tri-stated and the device enters a reset

state.

The LOS function is disabled in 10-bit mode. The LOS defaults high in 10-bit mode.

The LOS signal is reset to low (signal detected) under the following conditions:

Table 13. LOS Reset Conditions

OPMODE

Condition

LOS

0 (BTS Mode)

No LCVs occur within a CPRI hyperframe

0

LOF (LOSS OF FRAME) DETECTION

LOF counter is provided through an LOF MDIO status register per CPRI Specification. The LOF function is

disabled in 10-bit mode. Under 8-bit mode, LOF will prevent the SCAN25100 DCM scheme from activating.

Delay calibration measurement can only be performed when LOF is low.

TEST MODES

Loop Back Modes

The SCAN25100 supports multiple loop back modes for testing device, link, and system operation. The line loop

back mode enables the user to check the integrity of the serial data transmission paths. The local loop back

verifies operation of the local board. When switching between normal mode and loopback modes, the receiver

must synchronize to the new data stream.

Loopback mode can be controlled through the LOOP[1:0] pins or via MDIO. Pulling LOOP[1:0] low enables

MDIO control of loopback functions.

Table 14. Loopback Control Bit Settings

LOOP[1]

LOOP[0]

Loop Back Mode

0

0

Normal mode—no loop back (enable software program mode)

0

1

Line (remote) loop back mode

1

0

Local loop back mode

1

1

Special line (remote) loop back

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