Product Preview

DS21Q55

7. CLOCK MAP

Figure 9-1 shows the clock map of the DS21Q55. The routing for the transmit and receive clocks are shown for the various loopback modes and jitter attenuator positions. Although there is only one jitter attenuator, which can be placed in the receive or transmit path, two are shown for simplification and clarity.

CLOCK MAP Figure 9-1

MCLK

PRE-SCALER LIC4.MPS0LIC4.MPS1

2.048 TO 1.544 LIC2.3

SYNTHESIZER

 

 

 

 

DJA = 1

LOCAL

JITTER ATTENUATOR

 

DJA = 0

 

 

LOOPBACK

SEE LIC1 REGISTER

REMOTE

FRAMER

 

 

 

RCL = 1

 

JAS = 0

LOOPBACK

LOOPBACK

 

 

 

LLB = 0

 

AND

 

 

RXCLK

LTCA

DJA = 0

 

FLB = 0

 

 

RCL = 0

 

 

 

RECEIVE

LLB = 1

 

JAS = 1

 

FRAMER

TO

 

 

FLB = 1

JAS = 0

OR

 

LIU

DJA = 1

 

 

OR

 

 

 

 

 

 

 

DJA = 1

 

RLB = 1

 

TXCLK

 

 

 

 

LTCA

 

TRANSMIT

 

 

 

 

JAS = 1

 

RLB = 0

FORMATTER

 

AND

 

 

 

DJA = 0

 

 

 

8 x PLL

PAYLOAD

LOOPBACK

(SEE NOTES)

PLB = 1

PLB = 0

8XCLK

BPCLK

BPCLK

SYNTH

 

 

RCLK

TCLK

MUX

A B C

TCLK

The TCLK MUX is dependent on the state of the TCSS0 and TCSS1 bits in the LIC1 register and the state of the TCLK pin.

TCSS1

TCSS0

TRANSMIT CLOCK SOURCE

0

0

The TCLK pin (C) is always the source of Transmit Clock.

01 Switch to the recovered clock (B) when the signal at the TCLK pin fails to transition after 1 channel time.

10 Use the scaled signal (A) derived from MCLK as the Transmit Clock. The TCLK pin is ignored.

1

1

Use the recovered clock (B) as the Transmit Clock. The TCLK pin is ignored.

42 of 248

012103

Please contact telecom.support@dalsemi.com or search http://www.maxim-ic.com for updated

information.

Page 42
Image 42
Maxim DS21Q55 specifications Clock MAP Figure, Transmit Clock Source