Motorola MSC8101 ADS User's Guide Page 185

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Specifying the ALU Modes
Enhanced Filter Coprocessor (EFCOP) 9-9
Figure 9-2. IIR Filter Block Diagram
Multichannel mode for the IIR filter type works exactly the same way as for FIR filter type
as explained in Section 9.2.1.2, Multichannel Mode, on page 9-4. Decimation and
Adaptive modes are not available with the IIR filter type.
Initialization is always disabled with the IIR filter type, and the FCTL[8]:FPRC bit is
ignored. Thus, the SC140 core must write the initial input values to the FDM before the
EFCOP is enabled. The first value written to the FDIR is always the first sample to be
filtered.
9.4 Specifying the ALU Modes
Two modes that affect the arithmetic operation of the EFCOP are rounding and input
scaling. These ALU modes are independent of the filter type.
9.4.1 Rounding
Rounding mode is selected via the FACR[12–13]:FRM bits. These bits select the type of
rounding performed by the EFCOP data ALU (DALU) during arithmetic operations. The
EFCOP DALU performs the following types of rounding:
Convergent rounding (FACR[12–13]:FRM = 00)
Twos complement rounding (FACR[12–13]:FRM = 01)
No rounding, that is, truncation (FACR[12–13]:FRM = 10)
FDIR
FCMFDM
FDOR
A
0
A
1
A
2
A
N
y(n-1)
y(n-2)
y(n-3)
y(n-N)
Scale here
if FISL = 0
Scale here
if FISL = 1
w(n)
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