AD73322AST datasheet(36/43 Pages) AD

36 / 43 page

AD73322

–36–

REV. B

The circular buffer approach can be useful if a long initialization

sequence is required. The list of initialization words is put into

the buffer in the required order.

.VAR/DM/RAM/CIRC

init_cmds[16];

{Codec init sequence}

.VAR/DM/RAM

stat_flag;

.INIT

init_cmds:

b # 1 0 0 0 1 0 0 1 0 0 0 0 0 1 0 0 ,

b # 1 0 0 0 0 0 0 1 0 0 0 0 0 1 0 0 ,

b # 1 0 0 0 1 0 1 0 1 1 1 1 1 0 0 1 ,

b # 1 0 0 0 0 0 1 0 1 1 1 1 1 0 0 1 ,

b # 1 0 0 0 1 0 1 1 0 0 0 0 0 0 0 0 ,

b # 1 0 0 0 0 0 1 1 0 0 0 0 0 0 0 0 ,

b # 1 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 ,

b # 1 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 ,

b # 1 0 0 0 1 1 0 1 0 0 0 0 0 0 0 0 ,

b # 1 0 0 0 0 1 0 1 0 0 0 0 0 0 0 0 ,

b # 1 0 0 0 1 1 1 0 0 0 0 0 0 0 0 0 ,

b # 1 0 0 0 0 1 1 0 0 0 0 0 0 0 0 0 ,

b # 1 0 0 0 1 1 1 1 0 0 0 0 0 0 0 0 ,

b # 1 0 0 0 0 1 1 1 0 0 0 0 0 0 0 0 ,

b # 1 0 0 0 1 0 0 0 0 0 0 1 0 0 0 1 ,

b # 1 0 0 0 0 0 0 0 0 0 0 1 0 0 0 1 ;

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 AD73322. 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 ac-

cessed, it indicates that the initialization phase is complete. This

can be done “manually” in the DSP using a simple address

check or autobuffered mode can be used to the complete trans-

fer 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 AD73322 is effectively a cascade of two codec units, it is

important to observe some restrictions in the sequence of send-

ing initialization words to the two codecs. It is preferable to send

pairs of control words for the corresponding control registers 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 AD73322

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 inter-

rupt is generated during each sampling interval.

AD73322AST датащи(PDF) 36 Page - Analog Devices

AD73322AST датащи(HTML) 36 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43

датащи скачать

ссылки URL