Freescale Semiconductor MCF52277 Reference Manual page 101

Figure 4-7 and Figure 4-8
40-bit product used for accumulation, and 48-bit accumulator formats.
Product
Extended Product
Accumulator
Product
Extended Product
Accumulator
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:
if MACSR[6:5] == 00
Complete Accumulator[47:0] = {ACCextn[15:0], ACCn[31:0]}
if MACSR[6:5] == 01 or 11 /* signed fractional mode */
Complete Accumulator [47:0] = {ACCextn[15:8], ACCn[31:0], ACCextn[7:0]}
if MACSR[6:5] == 10
Complete Accumulator[47:0] = {ACCextn[15:0], ACCn[31:0]}
The four accumulators are represented as an array, ACCn, where n selects the register.
Freescale Semiconductor
show relative alignment of input operands, the full 64-bit product, the resulting
OperandY
X OperandX
40
8
+
8
Extension Byte Upper [7:0]
Figure 4-7. Fractional Alignment
OperandY
X OperandX
24
+
Extension Byte Upper [7:0]
Figure 4-8. Signed and Unsigned Integer Alignment
/* signed integer mode */
/* unsigned integer mode */
MCF52277 Reference Manual, Rev. 1
Enhanced Multiply-Accumulate Unit (EMAC)
32
32
23
40
40
Accumulator [31:0]
32
32
8 32
8 8 32
8 8 32
Accumulator [31:0]
Extension Byte Lower [7:0]
0
8
Extension Byte Lower [7:0]
4-9