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DA(15:0),

DB(15:0),

PHSTR

D Q

input

pointer

generation

PLLLOCK

MUX

CLK1

CLK1C

{PLLVDD,

inv_plllock, dual_clk}

MUX

clock

generator

resynchonized

da(15:0), db(15:0)

and phstr

sync source

{TXENABLE, PHSTR, QFLAG, DB(15),

DA(15) oneshot, SIF write, always off}

CLK2

CLK2C

PLL VCO

fifo_bypass

in_sel_d

in_sel_c

in_sel_b

in_sel_a

q_b

q_c

q_d

q_in

q_out

clk_in

clk_out

sel_q_a

sel_q_d

sel_q_c

sel_q_b

sync

D Q

DA(15:0),

DB(15:0),

PHSTR

D Q

output

pointer

generation

DA(15) oneshot

q_a

DAC5687-EP

SGLS333 – JUNE 2006

Figure 50. DAC5687 Input FIFO Logic

Initialization of the FIFO block involves selecting and asserting a synchronization source. Initialization causes the

input and output pointers to be forced to an offset of 2; the input pointer will be forced to the in_sel_a state while

the output pointer will be forced to the sel_q_c state. This initialization of the input and output pointers can cause

discontinuities in a data stream and should therefore be handled at startup.

Table 11. Synchronization Source Selection

sync_fifo (2:0)

Synchronization Source

000

txenable pin

001

phstr pin

010

qflag pin

011

db(15)

100

da(15) first transition (one shot)

101

sync now with SIF write (always on)

110

sync source disabled (always off)

111

sync now with SIF write (always on)

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