AD6654SLASHPCB datasheet(67/88 Pages) AD

67 / 88 page

AD6654

Rev. 0 | Page 67 of 88

PROGRAMMING INDIRECT ADDRESSED REGISTERS

USING SERIAL PORT

This section gives examples for programming CRCF coefficient

RAM (with an indirect addressing scheme) using the serial port

(either SPI or SPORT modes). Though the following specific

examples are for CRCF coefficient RAM programming, they can

be extended to other indirect addressed registers like DRCF

coefficient RAM. There are four possible programming scenarios,

and examples are given for all scenarios using two commands:

SerialWrite(data) and SerialRead. These commands signify an 8-

bit write to, or an 8-bit read from, the serial port (SPI or SPORT).

SerialWrite(8-bit number):

is an 8-bit write to SPI or SPORT. In

SPI mode, the SCLK is toggled eight times while SCS is pulled low.

In SPORT mode, SCS is pulled low, SRFS is held high for one

SCLK cycle, and eight bits of data are shifted into the SDI pin

following the SRFS pulse. Though the 8-bit number argument

shown in the following code is always shown MSBFIRST, it is

written with MSB shifting into the device first in MSBFIRST

mode, and it is written with LSB shifting into the device first in

LSBFIRST mode.

SerialRead():

is an 8-bit read from the SDO pin in SPI or SPORT

modes. In SPI mode, the SCLK toggles eight times while SCS is

low. In SPORT mode, SCS is pulled low, STFS is held high for one

SCLK cycle, and then the eight bits of data that shifted out on

SDO following the STFS pulse are read. The data shifted out

should be interpreted based on the polarity of the MSBFIRST pin.

MSBFIRST Mode Using Single Byte Block Transfers

SerialWrite(0x98); //CRCF Start Address

SerialWrite(0x01);

SerialWrite(0x00);

SerialWrite(0x99); //CRCF Final Address

SerialWrite(0x01);

SerialWrite(N-1);

//N is the number of coefficients

for (i=0 ; i < N; i++) {

//writing registers

SerialWrite(0x9E);

//MSB written first

SerialWrite(0x01);

//data bits[23:16]

SerialWrite(coeff[i] >> 16 & 0xFF);

SerialWrite(0x9D);

SerialWrite(0x01);

//data bits[15:8]

SerialWrite(coeff[i] >> 8 & 0xFF);

SerialWrite(0x9C);

//LSB written last

SerialWrite(0x01);

//data bits[7:0]

SerialWrite(coeff[i] & 0xFF);

}

SerialWrite(0x98); //CRCF Start Address

SerialWrite(0x01);

SerialWrite(0x00);

SerialWrite(0x99); //CRCF Final Address

SerialWrite(0x01);

SerialWrite(N-1);

//N is the number of coefficients

for (i=0 ; i < N; i++) {

//reading registers

SerialWrite(0x9E);

//MSB readback first

SerialWrite(0x81);

//data bits[23:16]

Coeff[i] = SerialRead() << 16;

SerialWrite(0x9D);

SerialWrite(0x81);

//data bits[15:8]

Coeff[i] |= SerialRead() << 8;

SerialWrite(0x9C);

//LSB readback last

SerialWrite(0x81);

//data bits[7:0]

Coeff[i] |= SerialRead();

}

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