2 Computational Units
2 – 18
2.3.2.2 Input Formats
To facilitate multiprecision multiplications, the multiplier accepts X and Y
inputs represented in any combination of signed twos-complement format
and unsigned format.
X input Y input
signed x signed
unsigned x signed
signed x unsigned
unsigned x unsigned
The input formats are specified as part of the instruction. These are
dynamically selectable each time the multiplier is used.
The (signed x signed) mode is used when multiplying two signed single
precision numbers or the two upper portions of two signed multiprecision
numbers.
The (unsigned x signed) and (signed x unsigned) modes are used when
multiplying the upper portion of a signed multiprecision number with the
lower portion of another or when multiplying a signed single precision
number by an unsigned single precision number.
The (unsigned x unsigned) mode is used when multiplying unsigned
single precision numbers or the non-upper portions of two signed
multiprecision numbers.
2.3.2.3 MAC Input/Output Registers
The sources of MAC input and output are:
Source for Source for Destination for
X input port Y input port R output port
MX0, MX1 MY0, MY1 MR (MR2, MR1, MR0)
AR MF MF
MR0, MR1, MR2
SR0, SR1
2.3.2.4 MR Register Operation
As described, and shown on the block diagram, the MR register is divided
into three sections: MR0 (bits 0-15), MR1 (bits 16-31), and MR2 (bits 32-
39). Each of these registers can be loaded from the DMD bus and output to
the R bus or the DMD bus.
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