AD1843JS datasheet(40/64 Pages) AD

40 / 64 page

REV. 0

–40–

AD1843

res

Reserved for future expansion. To ensure future compatibility, write “0” to all reserved bits.

Initial default state after reset: 0000 0000 0000 0000 (0000 hex). Cleared to default and cannot be written to when:

the RESET pin is asserted LO; when the PWRDWN pin is asserted LO; or when the G1EN bit in Control Register

Address 28 is reset to “0” (clock generator 1 disabled).

Address 19

Clock Generator 2 Control—Mode

Data 15

Data 14

Data 13

Data 12

Data 11

Data 10

Data 9

Data 8

C2REF

C2VID

C2PLLG

C2P200

C2X8/7

C2C128

res

Data 7

Data 6

Data 5

Data 4

Data 3

Data 2

Data 1

Data 0

C2M7

C2M6

C2M5

C2M4

C2M3

C2M2

C2M1

C2M0

C2REF

Clock Generator 2 Reference Select. Selects the fundamental clock reference used by Clock Generator 2 to

synthesize its “Conversion” (sample) and “Bit” clock rates.

0 = Clocks are referenced to the input on pin XTALI (crystal or master clock input).

Sample clock frequency is defined by Control Register Address 20 and Bit C2X8/7.

Sample clock phase may be shifted by Control Register Address 21.

Bit clock frequency is defined by bits C2M7:0 and C2P200.

Bit C2VID is ignored.

1 = Clocks are referenced to the input on pin SYNC2 (Sync 2 Clock Input).

Sample clock frequency is defined by C2VID and C2M7:0.

Sample clock phase is locked to SYNC2 and cannot be shifted.

Bit clock frequency is defined by bits C2M7:0 and C2P200 unless in Video Lock Mode (C2VID set to “1”)

where the Bit clocks are not produced.

Control Register Addresses 17, 18 and the C2X8/7 bit are ignored.

C2VID

Clock Generator 2 Video Lock Mode. This bit is used to select between lock modes when the Clock Generator 2 is

referenced to SYNC2 (C2REF set to “1”). This bit should be reset to “0” if C2REF is reset to “0.” When reset to

“0,” Clock Generator 2 is in normal lock mode where the Conversion clock will be frequency and phase locked to

SYNC2, and the Bit clock frequency is chosen using bits C2M7:0 and C2P200. When set to “1,” Clock Generator 2

is in video lock mode, where the Conversion clock frequency is selected using bits C2M7:0, and a Bit clock is not produced.

C2PLLG

Clock Generator 2 PLL Loop Gain Select. If reset to “0,” this bit selects finite PLL loop gain, and if set to “1,” this

bit selects infinite PLL loop gain. This bit should nominally be reset to “0.” Setting it to “1” may enhance the PLL’s

ability to lock to certain SYNC2 inputs, but it may also increase conversion noise.

C2P200

Clock Generator 2 Bit Clock +200 Frequency Modifier. When set to “1,” the Bit clock driven out of pin BIT2 will

have a frequency that is 200 Hertz greater than the frequency selected through bit C2M7:0. This bit is ignored when

in Video Lock Mode (C2VID set to “1”). C2P200 only modifies the bit clock driven on the BIT2 pin.

C2X8/7

Clock Generator 2 Conversion Clock 8/7 Frequency Modifier. When set to “1,” the Conversion clock frequency gen-

erated will be 8/7 times the value programmed in Control Register Address 20. This bit is ignored when clocks are

referenced to SYNC2 (C2REF set to “1”).

C2C128

Clock Generator 2 Conversion Clock Pin (CONV2) Frequency Select. When set to “1,” the frequency driven on to

the CONV2 pin will be 128 times the conversion rate. When reset to “0,” the frequency driven on to the CONV2 pin

will be the same as the conversion rate. C2C128 only modifies the clock frequency driven on the CONV2 pin.

res

Reserved for future expansion. To ensure future compatibility, write “0” to all reserved bits.

C2M7:0

Clock Generator 2 Clock Rate Modifiers.

When not in Video Lock Mode (C2REF and C2VID are not both set to “1”):

Bits C2M7:0 select the Bit clock rate which will be driven out on pin BIT2. Using the following table, the least sig-

nificant four bits (C2M3:0) are programmed to the desired Bit clock rate, and the most significant four bits

overwritten even if all previously programmed phase advance/retard has not been processed. When written, the con-

tents of this register (just prior to the write) are transmitted during slot 1 of the following frame (as with all Control

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