LF43168
DEVICES INCORPORATED
Dual 8-Tap FIR Filter
T
ABLE
1.
BITS
0–3
ACCEN — Accumulate Enable
When ACCEN is HIGH, both accumu-
lators are enabled for accumulation
and writing to the accumulator output
registers is disabled (the registers hold
their values). When ACCEN goes
LOW, accumulation is halted (by
sending zeros to the accumulator
feedback inputs) and writing to the
accumulator output registers is
enabled. This signal is latched on the
rising edge of CLK.
MUX
1-0
— Mux/Adder Control
MUX
1-0
controls the Mux/Adder as
shown in Table 3. Data is latched on
the rising edge of CLK.
OEL — Output Enable Low
When OEL is LOW, OUT
8-0
is enabled
for output and INB
9-1
can not be used.
When OEL is HIGH, OUT
8-0
is placed
in a high-impedance state and INB
9-1
is available for data input.
OEH — Output Enable High
When OEH is LOW, OUT
27-9
is
enabled for output. When OEH is
HIGH, OUT
27-9
is placed in a high-
impedance state.
FUNCTIONAL DESCRIPTION
Control Registers
There are two control registers which
determine how the LF43168 is config-
ured. Tables 1 and 2 show how each
register is organized. Data on CIN
9-0
is latched into the addressed control
register on the rising edge of WR.
Address data is input on A
8-0
. Con-
trol Register 0 is written to using
address 000H. Control Register 1 is
written to using address 001H (Note
that addresses 002H to 0FFH are
reserved and should not be written
to). When a control register is written
to, a reset occurs which lasts for 6 CLK
cycles from when WR goes HIGH.
This reset does not alter any data in
the coefficient banks. Control data
can be loaded asynchronously to CLK.
C
ONTROL
R
EGISTER
0 – A
DDRESS
000H
FUNCTION
DESCRIPTION
No Decimation, Delay by 1
Decimate by 2, Delay by 2
Decimate by 3, Delay by 3
Decimate by 4, Delay by 4
Decimate by 5, Delay by 5
Decimate by 6, Delay by 6
Decimate by 7, Delay by 7
Decimate by 8, Delay by 8
Decimate by 9, Delay by 9
Decimate by 10, Delay by 10
Decimate by 11, Delay by 11
Decimate by 12, Delay by 12
Decimate by 13, Delay by 13
Decimate by 14, Delay by 14
Decimate by 15, Delay by 15
Decimate by 16, Delay by 16
Decimation Factor/
0000 =
Decimation Register Delay Length 0001 =
0010 =
0011 =
0100 =
0101 =
0110 =
0111 =
1000 =
1001 =
1010 =
1011 =
1100 =
1101 =
1110 =
1111 =
Filter Mode Select
Coefficient Symmetry Select
FIR Filter A: Odd/Even Taps
FIR Filter B: Odd/Even Taps
FIR Filter B Input Source
Interleaved/Non-Interleaved
Coefficient Sets
4
5
6
7
8
9
0 = Single Filter Mode
1 = Dual Filter Mode
0 = Even-Symmetric Coefficients
1 = Odd-Symmetric Coefficients
0 = Odd Number of Filter Taps
1 = Even Number of Filter Taps
0 = Odd Number of Filter Taps
1 = Even Number of Filter Taps
0 = Input from INA
9-0
1 = Input from INB
9-0
0 = Non-Interleaved Coefficient Sets
1 = Interleaved Coefficient Sets
Bits 0-3 of Control Register 0 control
the decimation registers. The decima-
tion factor and decimation register
delay length is set using these bits.
Bit 4 determines if FIR filters A and B
operate separately as two filters or
together as one filter. Bit 5 is used to
select even or odd-symmetric coeffi-
cients. Bits 6 and 7 determine if there
are an even or odd number of taps in
filters A and B respectively. When the
FIR filters are set to operate as two
separate filters, bit 8 selects either
INA
9-0
or INB
9-0
as the filter B input
source. Bit 9 determines if the coeffi-
cient set used is interleaved or non-
interleaved (see Interleaved Coeffi-
cient Filters section). Most applica-
tions use non-interleaved coefficient
sets (bit 9 set to “0”).
Bits 0 and 1 of Control Register 1
determine the input and coefficient
data formats respectively for filter A.
Bits 2 and 3 determine the input and
coefficient data formats respectively
for filter B. Bit 4 is used to enable or
disable data reversal on the reverse
decimation path. When data reversal
is enabled, the data order is reversed
before being sent to the reverse
decimation path. Bits 5-8 select where
rounding will occur on the output
data (See Mux/Adder section). Bit 9
enables or disables output rounding.
Coefficient Banks
The coefficient banks supply coeffi-
cient data to the multipliers in both
FIR filters. The LF43168 can store 32
different coefficient sets. A coefficient
Video Imaging Products
4
03/28/2000–LDS.43168-H
LOGIC [ LOGIC DEVICES INCORPORATED ]
