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Data Sheet

AD9545

Rev. A | Page 111 of 157

TAGGED TIME STAMPS

A tagged time stamp is a time stamp with a special marker, or

tag, attached to it. Tagged time stamps allow the AD9545 to

embed a lower frequency clock within a higher frequency clock.

For example, by tagging every 10th edge of a clock signal, there

is a carrier signal (that is, the original clock signal) and a divide

by 10 version of the carrier embedded within it as a result of the

tagged time stamps.

The various time stamp sources within the AD9545 are capable

of generating tagged time stamps (the auxiliary NCOs, for

example). Likewise, certain time stamp destinations within the

AD9545 are capable of processing only tagged time stamps

while ignoring untagged time stamps (the user time stamp

processors, for example). However, the two DPLLs are the most

important of the time stamp destinations capable of using

tagged time stamps (see the Time Stamp Tagging Options

section).

Tagged Auxiliary NCO Time Stamps

The auxiliary NCOs generate time stamps coincident with the

expiration of each period defined by the programmed auxiliary

NCO frequency (that is, at the rollover point of the phase

accumulator). For example, a NCO frequency of 100 Hz results

in the generation of time stamps at a 100 Hz rate with each time

stamp 10 ms greater than the previous one.

The time stamp generator gives the user the option of tagging

auxiliary NCO time stamps via the 16-bit auxiliary NCO x tag ratio

bit fields (where x is 0 or 1) in Register 0x280B to Register 0x280C

and Register 0x284B to Register 0x284C.

The value represented by the auxiliary NCO x tag ratio bit field,

N, results in every Nth time stamp being tagged. That is,

auxiliary NCO x tag ratio = 1 means every other time stamp is

tagged, auxiliary NCO x tag ratio = 2 means every third time

stamp is tagged, 3 means every fourth time stamp is tagged, 4

means every fifth time stamp is tagged, and this pattern

continues up to 65,535. Note that auxiliary NCO x tag ratio = 0

(default) disables time stamp tagging (no tags).

The user can also shift the time position of the tagged flags via

the 16-bit auxiliary NCO x tag delta bit fields (where x is 0 or 1)

in Register 0x280D to Register 0x280E and Register 0x284D to

autoclearing bit fields. The value represented by the auxiliary

NCO x tag delta bit field, K, is a signed integer (twos

complement) indicating a number of fundamental periods of

the auxiliary NCO. Thus, for K = −3, the time stamp processor

tags time stamps three time stamps earlier than the Nth time

stamp locations indicated by the auxiliary NCO x tag ratio

value. K is effectively a phase shift of the tagged time stamp

period, where K < N.

Note that when the auxiliary NCO is the reference to the DPLL

for an active translation profile (see the Translation Profiles

section), shifting the time position of a tag is not valid and must

be avoided. When using the tag shift feature, be sure that any

translation profiles using the auxiliary NCO as a DPLL

reference are not enabled, or if they are enabled, that the

associated DPLL is in freerun or holdover mode.

Tagged Reference Time Stamps

Tags associated with time stamps originating from the reference

TDCs are the result of demodulating an embedded clock (see

the Distribution Embedded Output Clock Modulation section).

Sync events associated with demodulation generate tagged time

stamps. The user can program the DPLL to use the tagged time

stamps from a reference TDC.

Tagged Feedback Time Stamps

Tagged time stamps originating from the DPLL feedback path

are the result of sync events associated with the modulation

controller (see the Modulation Sync ssection). The user can

program the DPLL to use the tagged time stamps from a

feedback TDC.

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