Multiply-Accumulate Unit (MAC)
MCF52110 ColdFire® Integrated Microcontroller Reference Manual, Rev. 1
Freescale Semiconductor
4-9
Preliminary
4.3.3
MAC Instruction Execution Times
The instruction execution times for the MAC can be found in
Section 3.3.5.6, “MAC Instruction Execution
.
4.3.4
Data Representation
MACSR[S/U,F/I] selects one of the following three modes, where each mode defines a unique operand
type:
1. Two’s complement signed integer: In this format, an N-bit operand value lies in the range -2
(N-1)
< operand < 2
(N-1)
- 1. The binary point is right of the lsb.
2. Unsigned integer: In this format, an N-bit operand value lies in the range 0 < operand < 2
N
- 1. The
binary point is right of the lsb.
3. Two’s complement, signed fractional: In an N-bit number, the first bit is the sign bit. The remaining
bits signify the first N-1 bits after the binary point. Given an N-bit number,
a
N-1
a
N-2
a
N-3
... a
2
a
1
a
0
,
its value is given by the equation in
.
Eqn. 4-3
This format can represent numbers in the range -1 < operand < 1 - 2
(N-1)
.
For words and longwords, the largest negative number that can be represented is -1, whose internal
representation is 0x8000 and 0x8000_0000, respectively. The largest positive word is 0x7FFF or (1 - 2
-15
);
the most positive longword is 0x7FFF_FFFF or (1 - 2
-31
).
4.3.5
MAC Opcodes
MAC opcodes are described in the
ColdFire Programmer’s Reference Manual
.
Remember the following:
•
Unless otherwise noted, the value of MACSR[N,Z] is based on the result of the final operation that
involves the product and the accumulator.
•
The overflow (V) flag is managed differently. It is set if the complete product cannot be represented
as a 32-bit value (this applies to 32
×
32 integer operations only) or if the combination of the
product with the accumulator cannot be represented in the given number of bits. This indicator is
Load MACSR
move.l {Ry,#imm},MACSR
Writes a value to MACSR
Store MACSR
move.l MACSR,Rx
Write the contents of MACSR to a CPU register
Store MACSR to CCR
move.l MACSR,CCR
Write the contents of MACSR to the CCR
Load MAC Mask Reg
move.l {Ry,#imm},MASK
Writes a value to the MASK register
Store MAC Mask Reg
move.l MASK,Rx
Writes the contents of the MASK to a CPU register
Table 4-6. MAC Instruction Summary (continued)
Command
Mnemonic
Description
value
1 a
N
1
–
⋅
(
)
–
2
i
1
N
–
+
(
)
–
ai
⋅
i
0
=
N
2
–
∑
+
=
