AD6654SLASHPCB datasheet(44/88 Pages) AD

44 / 88 page

AD6654

Rev. 0 | Page 44 of 88

PROGRAMMING DRCF REGISTERS FOR

AN ASYMMETRICAL FILTER

To program the DRCF registers for an asymmetrical filter:

Write NTAPS – 1 in the DRCF taps register, where

NTAPS is the number of filter taps. The absolute

maximum value for NTAPS is 64 in asymmetrical filter

mode.

Write 0 for the DRCF coefficient offset register.

Write 0 for the symmetrical filter bit in the DRCF control

Write the start address for the coefficient RAM, typically

equal to the coefficient offset register in the DRCF start

address register.

In the DRCF stop address register, write the stop address

for the coefficient RAM, typically equal to the following:

Coefficient Offset + NTAPS − 1

Write all coefficients in reverse order (start with last

coefficient) to the DRCF coefficient memory register. If in

8-bit microport mode or serial port mode, write the lower

byte of the memory register first and then the higher byte.

After each write access to the DRCF coefficient memory

with the start address and ending with the stop address.

Note that each write or read access increments the internal

RAM address. Therefore, all coefficients should be read first

before reading them back. Also, for debugging purposes, each

RAM address can be written individually by making the start

and stop addresses the same. Therefore, to program one RAM

location, the user writes the address of the RAM location to

both the start and stop address registers, and then writes the

coefficient memory register.

PROGRAMMING DRCF REGISTERS FOR A

SYMMETRIC FILTER

To program the DRCF registers for a symmetrical filter:

Write NTAPS – 1 in the DRCF taps register, where

NTAPS is the number of filter taps. The absolute

maximum value for NTAPS is 128 in symmetric filter

mode.

Write ceil(64 – NTAPS/2) for the DRCF coefficient offset

greater than or equal to the argument.

Write 1 for the symmetrical filter bit in the DRCF control

Write the start address for the coefficient RAM, typically

equal to coefficient offset register, in the DRCF start

address register.

Write the stop address for the coefficient RAM, typically

equal to ceil(NTAPS/2) – 1, in the DRCF stop address

Write all coefficients to the DRCF coefficient memory

towards the end of the filter. When coefficients are

numbered 0 to NTAPS – 1, the middle coefficient is given

by the coefficient number ceil(NTAPS/2). If in 8-bit

microport mode or serial port mode, write the lower byte

of the memory register first and then the higher byte.

After each write access to the DRCF coefficient memory

with the start address and ending with the stop address.

Note that each write or read access increments the internal

RAM address. Therefore, all coefficients should be read first

before reading them back. Also, for debugging purposes, each

RAM address can be written individually by making the start

and stop addresses the same. Therefore, to program one RAM

location, the user writes the address of the RAM location to

both the start and stop address registers, and then writes the

coefficient memory register.

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