3.2.4. Accumulator and Output Cascade
- Addition or subtraction operation
- Biased rounding operation using a constant value of 2 N
- Dual channel accumulation
To dynamically perform addition or subtraction operation of the accumulator, control the negate input signal.
For biased rounding operation, you can specify and load a preset constant of 2 N before the accumulator module is enabled by specifying an integer to the parameter N value of preset constant. The integer N must be less than 64. You can dynamically enable or disable the use of the preset constant by controlling the loadconst signal. You can use this operation as an active muxing of the round value into the accumulator feedback path. The loadconst and the accumulate signals usage is mutually exclusive.
You can enable the double accumulator register using the parameter Enable double accumulator to perform double accumulation.
The accumulator module can support chaining of multiple DSP blocks for addition or subtraction operation by enabling chainin input port and chainout output port. In 18 × 18 systolic mode, only 44-bit of the chainin input bus and chainout output bus will be used. However, all 64-bit chainin input bus must be connected to the chainout output bus from the preceding DSP block.
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