DEVICES INCORPORATED
LF43168
Dual 8-Tap FIR Filter
4
Video Imaging Products
03/28/2000–LDS.43168-H
ACCEN — Accumulate Enable
When ACCEN is HIGH, both accumulators 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.
MUX1-0 — Mux/Adder Control
MUX1-0 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, OUT8-0 is enabled
for output and INB9-1 can not be used.
When OEL is HIGH, OUT8-0 is placed
in a high-impedance state and INB9-1
is available for data input.
OEH — Output Enable High
When OEH is LOW, OUT27-9 is
enabled for output. When OEH is
HIGH, OUT27-9 is placed in a highimpedance state.
FUNCTIONAL DESCRIPTION
Control Registers
There are two control registers which
determine how the LF43168 is configured. Tables 1 and 2 show how each
register is organized. Data on CIN9-0
is latched into the addressed control
register on the rising edge of WR.
Address data is input on A8-0. Control 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.
Bits 0-3 of Control Register 0 control
the decimation registers. The decimation 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 coefficients. 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
INA9-0 or INB9-0 as the filter B input
source. Bit 9 determines if the coefficient set used is interleaved or noninterleaved (see Interleaved Coefficient Filters section). Most applications 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 coefficient data to the multipliers in both
FIR filters. The LF43168 can store 32
different coefficient sets. A coefficient
BITS FUNCTION DESCRIPTION
0–3 Decimation Factor/ 0000 = No Decimation, Delay by 1
Decimation Register Delay Length 0001 = Decimate by 2, Delay by 2
0010 = Decimate by 3, Delay by 3
0011 = Decimate by 4, Delay by 4
0100 = Decimate by 5, Delay by 5
0101 = Decimate by 6, Delay by 6
0110 = Decimate by 7, Delay by 7
0111 = Decimate by 8, Delay by 8
1000 = Decimate by 9, Delay by 9
1001 = Decimate by 10, Delay by 10
1010 = Decimate by 11, Delay by 11
1011 = Decimate by 12, Delay by 12
1100 = Decimate by 13, Delay by 13
1101 = Decimate by 14, Delay by 14
1110 = Decimate by 15, Delay by 15
1111 = Decimate by 16, Delay by 16
4 Filter Mode Select 0 = Single Filter Mode
1 = Dual Filter Mode
5 Coefficient Symmetry Select 0 = Even-Symmetric Coefficients
1 = Odd-Symmetric Coefficients
6 FIR Filter A: Odd/Even Taps 0 = Odd Number of Filter Taps
1 = Even Number of Filter Taps
7 FIR Filter B: Odd/Even Taps 0 = Odd Number of Filter Taps
1 = Even Number of Filter Taps
8 FIR Filter B Input Source 0 = Input from INA9-0
1 = Input from INB9-0
9 Interleaved/Non-Interleaved 0 = Non-Interleaved Coefficient Sets
Coefficient Sets 1 = Interleaved Coefficient Sets
TABLE 1. CONTROL REGISTER 0 – ADDRESS 000H