2 Computational Units
2 – 6
The output of the ALU is loaded into either the ALU feedback (AF)
register or the ALU result (AR) register. The AF register is an ALU
internal register which allows the ALU result to be used directly as the
ALU Y input. The AR register can drive both the DMD bus and the R bus.
It is also loadable directly from the DMD bus. The instruction set also
provides for reading AR over the PMD bus, but there is no direct
connection; this operation uses the DMD-PMD bus exchange unit.
Figure 2.2 ALU Block Diagram
X Y
ALU
R
AZ
AN
AC
AV
AS
AQ
CI
MUXMUX
AR
REGISTER
MUX
MUX
16
AF
REGISTER
AX
REGISTERS
2 x 16
AY
REGISTERS
2 x 16
16
16
16
16
24
16
PMD BUS
DMD BUS
16 (UPPER)
R - BUS
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