PDSP16318/16318A
FUNCTIONAL DESCRIPTION
The PDSP16318 is a Dual 20-bit Adder/Subtractor
configuredtosupportComplexArithmetic. Thedevicemaybe
used with each of the adders allocated to real or imaginary
data (e.g. Complex Conjugation), the entire device allocated
to Real or Imaginary Data (e.g. Radix 2 Butterflys) or each of
the adders configured as accumulators and allocated to real
or imaginary data (Complex Filters). Each of these modes
ensures that a full 20MHz throughput is maintained through
both adders, the first and last mode illustrating true Complex
operation, where both real and imaginary data is handled by
the single device.
the accumulator registers. The PDSP16318 contains an 8-
cycle deskew register selected via the DEL control. This
deskew register is used in FFT applications to ensure correct
phasing of data that has not passed through the PDSP16112
Complex Multiplier.
The16-bitoutputsfromthePDSP16318arederivedfrom
the 20-bit result generated by the Adders. The three bit S2:0
input selects eight different shifted output formats ranging
from the most significant 16 bits of the 20-bit data, to the least
significant13bitsofthe20-bitdata. Inthismodethe14th,15th
and 16th bits of the output are set to zero. The shift selected
is applied to both adder outputs, and determines the function
of the OVR flag. The OVR flag becomes active when either of
the two adders produces a result that has more significant
digits than the MSB of the 16-bit output from the device. In this
manner all cases when invalid data appears on the output are
flagged.
Both Adder/Subtractors may be controlled
independently via the ASR and ASI inputs. These controls
permit A + B, A - B, B - A or pass A operations, where the A
input to the Adder is derived from the input multiplexer. The
CLR control line allows the clearing of both accumulator
registers. The two multiplexers may be controlled via the MS
inputs, to select either new input data, or fed-back data from
Symbol
A15:0
Type
Input
Input
Description
Data presented to this input is loaded into the input register on the rising edge of CLK. A15 is the MSB.
B15:0
Data presented to this input is loaded into the input register on the rising edge of CLK. B15 is the MSB
and has the same weighting as A15.
C15:0
D15:0
CLK
Output
Output
Input
New data appears on this output after the rising edge of CLK. C15 is the MSB.
New data appears on this output after the rising edge of CLK. C15 is the MSB.
Common Clock to all internal registers
Input
Clock enable: when low the clock to the A input register is enabled.
Clock enable: when low the clock to the B input register is enabled.
CEA
CEB
OEC
Input
Input
Output enable: Asynchronous 3-state output control: The C outputs are in a high impedance
state when this input is high.
Input
Output enable: Asynchronous 3-state output control: The D outputs are in a high impedance
state when this input is high.
OED
OVR
Output
Overflow flag: This flag will go high in any cycle during which either the output data overflows the number
range selected or either of the adder results overflow. A new OVR appears after the rising edge of the
CLK.
ASR1:0
ASI1:0
Input
Input
Input
Add/subtract Real: Control input for the 'Real' adder. This input is latched by the rising edge of clock.
Add/subtract Imag: Control input for the 'Imag' adder. This input is latched by the rising edge of clock.
Accumulator Clear: Common accumulator clear for both Adder/Subtractor units. This input is latched by
the rising edge of CLK.
CLR
MS
Input
Input
Input
Mux select: Control input for both adder multiplexers. This input is latched by the rising edge of CLK.
When high the feedback path is selected.
S2:0
DEL
Scaling control: This input selects the 16-bit field from the 20-bit adder result that is routed to the outputs.
This input is latched by the rising edge of CLK.
Delay Control: This input selects the delayed input to the real adder for operations involving the
PDSP16112. This input is latched by the rising edge of CLK.
VCC
GND
Power
+5V supply: Both Vcc pins must be connected.
0V supply: Both GND pins must be connected.
Ground
3
MITEL [ MITEL NETWORKS CORPORATION ]
