mcf51jf128 Freescale Semiconductor, Inc, mcf51jf128 Datasheet - Page 287

• Manufacturer Part Number: mcf51jf128
• Description: Mcf51jf128 Reference Manual
• Manufacturer: Freescale Semiconductor, Inc

The OEP stalls the store-accumulator instruction for two cycles: the EMAC pipeline
depth minus 1. The minus 1 factor is needed because the OEP and EMAC pipelines
overlap by a cycle, the AGEX stage. As the store-accumulator instruction reaches the
AGEX stage where the operation is performed, the recently updated accumulator 0 value
is available.
As with change or use stalls between accumulators and general-purpose registers,
introducing intervening instructions that do not reference the busy register can reduce or
eliminate sequence-related store-MAC instruction stalls. A major benefit of the EMAC is
the addition of three accumulators to minimize stalls caused by exchanges between the
accumulator(s) and general-purpose registers.
12.3.4 Data Representation
MACSR[S/U,F/I] selects one of the following three modes, where each mode defines a
unique operand type:
This format can represent numbers in the range -1 ≤ operand ≤ 1 - 2
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
2
12.3.5 MAC Opcodes
MAC opcodes are described in the ColdFire Programmer's Reference Manual.
Remember the following:
Freescale Semiconductor, Inc.
-31
1. Two's complement signed integer: In this format, an N-bit operand value lies in the
2. Unsigned integer: In this format, an N-bit operand value lies in the range 0 ≤ operand
3. Two's complement signed fractional: In an N-bit number, the first bit is the sign bit.
). . Thus, the number range for these signed fractional numbers is [-1.0, ..., 1.0].
range -2
≤ 2
The remaining bits signify the first N-1 bits after the binary point. Given an N-bit
number, a
equation.
N
- 1. The binary point is right of the lsb.
(N-1)
N-1
≤ operand ≤ 2
a
N-2
a
N-3
MCF51JF128 Reference Manual, Rev. 2, 03/2011
... a
2
a
(N-1)
1
a
-15
0
, its value is given by the equation in the following
- 1. The binary point is right of the lsb.
); the most positive longword is 0x7FFF_FFFF or (1 -
Preliminary
Chapter 12 Enhanced Multiply-Accumulate Unit (EMAC)
-(N-1)
.
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