AD6624SSLASHPCB datasheet(37/40 Pages) AD

37 / 40 page

REV. B

AD6624

–37–

EXTEST (3’b000) Places the IC into an external boundary-test

mode and selects the boundary-scan register to be connected

between TDI and TDO. During this, the boundary-scan regis-

ter is accessed to drive test data off-chip via boundary outputs

and receive test data off-chip from boundary inputs.

IDCODE (3’b001) Allows the IC to remain in its functional

mode and selects device ID register to be connected between

TDI and TDO. Accessing the ID register does not interfere

with the operation of the IC.

SAMPLE/PRELOAD (3’b010) Allows the IC to remain in

normal functional mode and selects the boundary-scan register

to be connected between TDI and TDO. The boundary-scan

the functional data entering and leaving the IC. Also, test

data can be preloaded into the boundary scan register before

an EXTEST instruction.

HIGHZ (3’b011) Sets all outputs to high impedance state.

Selects the 1-bit bypass register to be connected between

TDI and TDO.

CLAMP (3’b100) Sets the outputs of the IC to logic levels

determined by the boundary-scan register and selects the 1-bit

bypass register to be connected between TDI and TDO. Before

this instruction, boundary-scan data can be preloaded with

the SAMPLE/PRELOAD instruction.

BYPASS (3’b111) Allows the IC to remain in normal functional

mode and selects 1-bit bypass register between TDI and TDO.

During this instruction, serial data is transferred from TDI to

TDO without affecting operation of the IC.

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

variable address is the External Address A[2:0] and data is the

value to be placed in the external interface register.

Internal Address = 0x087

// holding registers for NCO phase byte wide access data

int d1, d0;

// NCO frequency word (16-bits wide)

NCO_PHASE = 0xCBEF;

// write ACR

write_micro(7, 0x03);

// write CAR

write_micro(6, 0x03);

// 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_FREQ & 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 transaction, the

high bytes of the data are moved from the internal address

pointed to by the CAR and AMR into the remaining data regis-

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

registers using the appropriate 3-bit addresses. The number 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

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