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AD9898

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EXTERNAL SYNCHRONIZATION (MASTER MODE)

External synchronization can be used to synchronize the VD

and HD signal by applying an external pulse on the SYNC/

VGATE pin (Pin 45) for master mode operation. The SYNC/

VGATE pin is configured as an external SYNC input for mas-

ter mode operation by setting the SLAVE_MODE register

(Addr 0xD6) = 0. (The AD9898 defaults to slave mode at

power-up.)

SYNCCNT (Addr 0x0A) and SYNCPOL (Addr 0x01) are the

only two registers used for configuring the AD9898 for external

synchronization. The SYNCPOL is a 1-bit register used for

configuring the SYNC input as either active low or active high.

The AD9898 defaults to active low at power-up. The function

of the SYNCCNT register is described in Table X. Figures 16

and 17 provide two examples of external synchronization with

SYNCPOL = 0.

Table X. External Synchronization (Master Mode)

SYNCCNT

External Synchronization Options

0Disable External Synchronization

VD Sync at every SYNC Pulse

VD Sync after Second Applied SYNC Pulse

VD Sync after Third Applied SYNC Pulse

VD Sync after Fourth Applied SYNC Pulse

VD Sync after Fifth Applied SYNC Pulse

VD Sync after Sixth Applied SYNC Pulse

VD Sync after Seventh Applied SYNC Pulse

VD Sync after Eighth Applied SYNC Pulse

VD Sync after Ninth Applied SYNC Pulse

VD Sync after Tenth Applied SYNC Pulse

VD Sync after Eleventh Applied SYNC Pulse

VD Sync after Twelfth Applied SYNC Pulse

VD Sync after Thirteenth Applied SYNC Pulse

VD Sync after Fourteenth Applied SYNC Pulse

VD Sync after First Applied SYNC Pulse Only

2 CLIMIN

MODE A

MODE B

SERIAL

WRITES

OPERATION

MODE

4 CLI

CHANGE TO MODE B

SYNC

Figure 16. Example of Synchronization with SYNCPOL = 0 and SYNCCNT = 1

4 CLI

2 CLIMIN

SYNC

Figure 17. Example of Synchronization with SYNCPOL = 0 and SYNCCNT = 3

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