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MPC563XM Reference Manual, Rev. 1
896
Freescale Semiconductor
Preliminary—Subject to Change Without Notice
according to the algorithmic description below. SR shifting operation depends also on SHF or ALUOP
fields. ALUOP and SHF never exist both on the same microinstruction format.
SR Operation
:
SR[22:0] = SR[23:1];
if SHF == “01” or ALUOP == “10110” then
SR[23] = ALU_OUT[0];
else
SR[23] = 0;
endif;
Post-ALU Shift Operations
Post-ALU shift can be selected by SHF field (2 bits) or by some specific ALUOP field values. SHF and
ALUOP fields are never both available in the same microinstruction format. When selecting post-ALU
shift operation using ALUOP field, ALU will always add the sources before shifting the result.
Carry flag is only updated when CCS or CCSV[1:0] fields allow it (see
”). Algorithmic descriptions of post-ALU shift operations are presented in
Section 23.4.8.2.2, “ALU ADD Operation with and without shifting
”.
Table 23-69. Shift Register Control - SRC
SRC
Meaning
0
shift right SR 1 bit
1
no shift
Table 23-70. Post-ALU Shift Operation
Post ALU Operation
SHF
1
1
ALU performs AS+BS before shift/rotate for all SHF
values.
ALUOP
shift left (1 bit)
00
10101
shift right (1 bit)
01
10110
rotate right (1 bit)
10
10111
no shift/rotate
11
any other
2
2
some ALUOP combinations perform shift/rotate, but not
using the Post-ALU Shifter (see