AD73322LAST datasheet(33/40 Pages) AD

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AD73322L

–33–

and the DSP program initializes pointers to the top of the buffer

i3 = ^init_cmds;

l3 = %init_cmds;

and puts the first entry in the DSP’s transmit buffer so that it is

available at the first SDOFS pulse.

ax0 = dm(i3,m1);

tx0 = ax0;

The DSP’s transmit interrupt is enabled.

imask = b#0001000000;

At each occurrence of an SDOFS pulse, the DSP’s transmit

buffer contents are sent to the SDI pin of the AD73322L. This

also causes a subsequent DSP Tx interrupt which transfers the

initialization word, pointed to by the circular buffer pointer, to

the Tx buffer. The buffer pointer is updated to point to the next

unsent initialization word. When the circular buffer pointer wraps

around, which happens after the last word has been accessed, it

indicates that the initialization phase is complete. This can be done

“manually” in the DSP using a simple address check, or auto-

buffered mode can be used to complete the transfer automatically.

txcdat: ar = dm(stat_flag);

ar = pass ar;

if eq rti;

ena sec_reg;

ax0 = dm (i3, m1);

tx0 = ax0;

ax0 = i3;

ay0 = ^init_cmds;

ar = ax0 - ay0;

if gt rti;

ax0 = 0x00;

dm (stat_flag) = ax0;

rti;

In the main body of the program, the code loops waiting for the

initialization sequence to be completed.

check_init:

ax0 = dm (stat_flag);

af = pass ax0;

if ne jump check_init;

As the AD73322L is effectively a cascade of two codec units, it

is important to observe some restrictions in the sequence of

sending initialization words to the two codecs. It is preferable to

send pairs of control words for the corresponding control regis-

ters in each codec, and it is essential to send the control word

for codec 2 before that for codec 1. Control Registers A and

B contain settings, such as sampling rate, serial clock rate, etc.,

which critically require synchronous update in both codecs.

Once the device has been initialized, Control Register A on both

codecs is written with a control word which changes the operat-

ing mode from Program Mode to either data mode or Mixed

Control Data Mode. The device count field which defaults to

000b will have to be programmed to 001b for a single AD73322L

device. In data mode or mixed mode, the main function of the

device is to return ADC samples from both codecs and to accept

DAC words for both codecs. During each sample interval, two

ADC samples will be returned from the device, while in the same

interval two DAC update samples will be sent to the device. In

order to reduce the number of interrupts and to reduce com-

plexity, autobuffering can be used to ensure that only one

interrupt is generated during each sampling interval.

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