MPC563XM Reference Manual, Rev. 1
890
Freescale Semiconductor
Preliminary—Subject to Change Without Notice
Microinstructions With Fields ABSE and ABDE
In microinstructions where ABSE and ABDE fields are available (1 bit each), ABSE controls register set
selection for T4ABS and ABDE controls register set selection for T2ABD.
shows the
meaning of values for ABSE and ABDE fields.
Microinstructions Without Fields ABSE and ABDE
When ABSE and ABDE are not available in a microinstruction format, register set is selected by T4BBS
field.
explains how to select a register set either for T4ABS and T2ABD.
23.4.9.2.2
Selecting Sources and Destination
All ALU/MDU operations need 2 sources (called AS and BS) and 1 destination (called AD), except for
some of those that use immediate data (see
Section 23.4.9.2.11, “Operations With Immediate Data
”).
Fields T4ABS (4 bits), ABSE (1 bit), T4BBS (3 bits) select sources, while T2ABD (4 bits) and ABDE (1
bit) select the destination. When MDU is used (multiply/divide), T2ABD destination selection is ignored
and results are stored in MACH and MACL (see
Section 23.4.8.3, “MAC and Divide Unit (MDU)
”).
ABSE and ABDE are not available in some microinstruction formats that support ALU/MDU operations.
However, in all formats where ABSE is available, ABDE is also available and vice-versa. The existence
of ABSE/ABDE fields changes the meaning of T4BBS field, as shown in
. On instructions
with immediate data, it is used as B-source (see
Section 23.4.9.2.11, “Operations With Immediate Data
).
All sources and destinations have a size associated to it, and these sizes are used to select flag sample
position (see
Section 23.4.9.2.3, “Flags Sampling Control
”). Sizes can be 8, 16 or 24 bits. Registers that
are not exactly of one of these sizes are treated as the immediately upper size (e.g., CHAN[4:0] is an 8-bit
source). See
Section 23.4.9.2.3, “Flags Sampling Control
for more information.
Table 23-59. Register Set Selection by ABSE or ABDE
ABSE or ABDE
Register Set Selected
0
second
1
first
Table 23-60. Register Set Selection by T4BBS w/o ABSE,ABDE
T4BBS
Register Set For T2ABD
Register Set For T4ABS
0xx
first
first
100
second
second
101
second
first
110
first
second
111
first
first
none
1
1
refers to operations with immediate data as B-source, without ABSE,ABDE.
first
first
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