mcf51jf128 Freescale Semiconductor, Inc, mcf51jf128 Datasheet - Page 281

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

bit product is calculated and truncated or rounded to the most-significant 40-bit result
using the round-to-nearest (even) method before it is combined with the destination
accumulator.
For all operations, the resulting 40-bit product is extended to a 48-bit value (using sign-
extension for signed integer and fractional operands, zero-fill for unsigned integer
operands) before being combined with the 48-bit destination accumulator.
The following two figures show relative alignment of input operands, the full 64-bit
product, the resulting 40-bit product used for accumulation, and 48-bit accumulator
formats.
Therefore, the 48-bit accumulator definition is a function of the EMAC operating mode.
Given that each 48-bit accumulator is the concatenation of 16-bit accumulator extension
register (ACCextn) contents and 32-bit ACCn contents, the specific definitions are:
Freescale Semiconductor, Inc.
Extended Product
Extended Product
Accumulator
Accumulator
Product
Product
Figure 12-3. Signed and Unsigned Integer Alignment
Extension Byte Upper [7:0]
40
MCF51JF128 Reference Manual, Rev. 2, 03/2011
Extension Byte Upper [7:0]
X
Figure 12-2. Fractional Alignment
24
X
OperandX
OperandY
OperandY
OperandX
8
8
Preliminary
8
8
Extension Byte Lower [7:0]
40
40
8
8
8
Chapter 12 Enhanced Multiply-Accumulate Unit (EMAC)
Accumulator [31:0]
32
32
32
32
32
32
32
23
Accumulator [31:0]
Extension Byte Lower [7:0]
8
0
281