AD6635BBSLASHPCB datasheet(58/60 Pages) AD

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AD6635

INTERNAL WRITE ACCESS

Up to 20 bits of data (as needed) can be written by the process

described below. Any high order bytes that are needed are writ-

ten to the corresponding data registers defined in the external

3-bit address space. The least significant byte is then written to

DR0 at address (000). When a write to DR0 is detected, the

internal microprocessor port state machine then moves the data

in DR2–DR0 to the internal address pointed to by the address

in the LAR and AMR.

Write Pseudocode

void write_micro(ext_address, int data);

main();

{

/* This code shows the programming of the NCO

phase offset register using the write_micro

function as defined above. The variable address

is the External Address A[2:0]

and data is the

value to be placed in the external interface

Internal Address = 0x87

// holding registers for NCO phase byte wide

access data

int d1, d0;

// NCO phase word

(16-bits wide)

NCO_PHASE = 0xCBEF;

// write ACR

write_micro(7, 0x03 );

// write CAR

write_micro(6, 0x87);

// write DR1 with D[15:8]

d1 = (NCO_PHASE & 0xFF00) >> 8;

write_micro(1, d1);

// write DR0 with D[7:0]

// On this write all data is transferred to the

internal address

d0 = NCO_PHASE & 0xFF;

write_micro(0, d0);

}

// end of main

INTERNAL READ ACCESS

A read is performed by first writing the CAR and AMR, as with

a write. The data registers (DR2–DR0) are then read in the

reverse order that they were written. First, the least significant

byte of the data (D[7:0]) is read from DR0. On this transac-

tion, the high bytes of the data are moved from the internal

address pointed to by the CAR and AMR into the remaining

data registers (DR2–DR1). This data can then be read from the

data registers using the appropriate 3-bit addresses. The num-

ber of data registers used depends solely on the amount of data

to be read or written. Any unused bit in a data register should

be masked out for a read.

Read Pseudocode

int read_micro(ext_address);

main();

{

/* This code shows the reading of

the first

RCF coefficient using the read_micro function

as defined above. The variable address is the

External Address A[2..0].

Internal Address = 0x000

// holding registers for the coefficient

int d2, d1, d0;

// coefficient

(20-bits wide)

long coefficient;

// write AMR

write_micro(7, 0x00 );

// write LAR

write_micro(6, 0x00);

/* read D[7:0] from DR0,

All data is moved

from the Internal Registers to the interface

registers on this access

d0 = read_micro(0) & 0xFF;

// read D[15:8] from DR1

d1 = read_micro(1) & 0xFF;

// read D[23:16] from DR2

d2 = read_micro(2) & 0x0F;

coefficient = d0 + (d1 << 8) + (d2 << 16);

}

// end of main

AD6635BB/PCB Datasheet(PDF) 58 Page - Analog Devices

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