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Data Sheet

AD9545

Rev. A | Page 61 of 157

N-Shot Pattern Generation

An N-shot pattern consists of a specified clock segment and gap

segment per the 6-bit unsigned N-shot bit field and 8-bit unsigned

N-shot gap bit field, respectively. The N-shot bit fields reside in

N-shot gap bit fields reside in Register 0x10D2 and Register 0x14D2.

The clock and gap segment are in units of the Q divider output

period, as shown in Figure 50. The N-shot generator treats a

value of 0 for the N-shot bit field as clock segment = 0 and a

value of 0 for the N-shot gap bit field as gap segment = 1,

resulting in no output.

The N-shot generator is capable of burst or periodic operation.

To select burst or periodic operation, use the N-shot request

mode bit in Register 0x10D3, Bit 6, and Register 0x14D3, Bit 6.

When N-shot request mode = 0, the N-shot generators operate

in burst mode (see Figure 51). When N-shot request mode = 1,

the N-shot generators operate in periodic gapped mode (see

Figure 52).

In burst operation, the rising edge of the trigger signal constitutes

the trigger event. Prior to the burst, the generator is in its default

state (Logic 0), which it holds until triggered (see the N-Shot

Triggering section).

When triggered, the N-shot generator produces an output

sequence (see the bottom trace of Figure 50). At the end of the

sequence, the N-shot generator remains in its default state

(Logic 0).

In burst operation, the output appears as a sequence of Q divider

cycles per the N-shot bit field (where the clock segment = 6 in

Figure 50). The gap period (where the gap segment = 10 in

Figure 50) is effectively an extension of the default output

condition, which is the low state.

In periodic operation, the logic level of the trigger matters (rather

than the rising edge as in burst mode). The N-shot generator,

starting from its default state (Logic 0), waits for the trigger to

assume a Logic 1 state. At this point, the N-shot generator begins

repeatedly generating the burst pattern (clock segment pulses,

then gap segment pulses) per Figure 52. The N-shot generator

continues generating burst patterns until the trigger assumes a

Logic 0 state. The occurrence of the Logic 0 state informs the

generator to stop synchronously. That is, if the generator is not in

the gap portion of the burst, it stalls at the end of the current pulse

as shown in Figure 53. Furthermore, returning the trigger signal

to Logic 1 causes the pattern to resume from where it previously

stopped (that is, with the absent pulses shown in Figure 53).

Q DIVIDER

OUTPUT

CLOCK

OUTPUT

Q DIVIDER PERIOD BASED ON ITS INPUT CLOCK AND DIVIDE RATIO

CLOCK SEGMENT = 6

GAP SEGMENT = 10

TIME

Figure 50. N-Shot Plus Gap Clock Signal

Q DIVIDER

OUTPUT

CLOCK

OUTPUT

Q DIVIDER PERIOD (PER ITS INPUT CLOCK AND DIVIDE RATIO)

CLOCK SEGMENT = 6

GAP SEGMENT = 10

TRIGGER

BURST

RISING EDGE OF

TRIGGER INITIATES

BURST

BURST ENDS AFTER CLK AND GAP Q-DIVIDER CYCLES

TIME

Figure 51. Burst Clock Signal

CLOCK

OUTPUT

BURST

PATTERN

TRIGGER

FALLING EDGE

TERMINATES

PERIODIC BURST

START

PATTERN

GENERATION

BURST

PATTERN

BURST

PATTERN

BURST

PATTERN

BURST

PATTERN

TIME

Figure 52. Periodic Gapped Clock Signal

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