Adder; Accumulator And Chainout Adder - Altera Cyclone V Device Handbook

CV-52003
2014.01.10
There are two multipliers per variable precision DSP block. You can configure these two multipliers in
several operational modes:
One 27 x 27 multiplier
Two 18 (signed)/(unsigned) x 19 (signed) multipliers
Three 9 x 9 multipliers
Related Information
Operational Mode Descriptions
Provides more information about the operational modes of the multipliers.

Adder

You can use the adder in various sizes, depending on the operational mode:
One 64-bit adder with the 64-bit accumulator
Two 18 x 19 modes—the adder is divided into two 37-bit adders to produce the full 37-bit result of each
independent 18 x 19 multiplication
Three 9 x 9 modes—you can use the adder as three 18-bit adders to produce three 9 x 9 multiplication
results independently

Accumulator and Chainout Adder

The Cyclone V variable precision DSP block supports a 64-bit accumulator and a 64-bit adder.
The following signals can dynamically control the function of the accumulator:
NEGATE
LOADCONST
ACCUMULATE
The accumulator supports double accumulation by enabling the 64-bit double accumulation registers located
between the output register bank and the accumulator.
The double accumulation registers are set statically in the programming file.
The accumulator and chainout adder features are not supported in two independent 18 x 19 modes and
three independent 9 x 9 modes.
Table 3-3: Accumulator Functions and Dynamic Control Signals
This table lists the dynamic signals settings and description for each function. In this table, X denotes a "don't care"
value.
Function
Zeroing
Preload
Variable Precision DSP Blocks in Cyclone V Devices
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on page 3-10
Description
Disables the
accumulator.
Loads an initial value
to the accumulator.
Only one bit of the
64-bit preload value
can be "1". It can be
used as rounding the
DSP result to any
position of the 64-bit
result.
NEGATE LOADCONST
0 0
0 1
3-9
Adder
ACCUMULATE
0
0
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