Memory Map/Register Definition
MCF548x Reference Manual, Rev. 3
Freescale Semiconductor 4-7

Table 4-2 summarizes the interaction of the MACSR[S/U,F/I,R/T] control bits.

5 F/I Operational mode field: Fractional/integer mode Determines whether input operands are treated as
fractions or integers.
0 Integers can be represented in either signed or unsigned notation, depending on the value of S/U.
1 Fractions are represented in signed, fixed-point, two’s complement notation. Values range from
-1 to 1- 2-15 for 16-bit fractions and -1 to 1 - 2-31 for 32-bit fractions. See Section 4.3.2, “Data
Representation."
4 R/T Operational mode field: Round/truncate mode. Controls the rounding procedure for MOV.L
ACCx,Rx, or MSAC.L instructions when operating in fractional mode.
0 Truncate. The product’s lsbs are dropped before it is combined with the accumulator. Additionally,
when a store accumulator instruction is executed (MOV.L ACCx,Rx), the 8 lsbs of the 48-bit
accumulator logic are simply truncated.
1 Round-to-nearest (even). The 64-bit product of two 32-bit, fractional operands is rounded to the
nearest 40-bit value. If the low-order 24 bits equal 0x80_0000, the upper 40 bits are rounded to
the nearest even (lsb = 0) value.See Section 4.2.1.1.1, “Rounding.” Additionally, when a store
accumulator instruction is executed (MOV.L ACCx,Rx), the lsbs of the 48-bit accumulator logic are
used to round the resulting 16- or 32-bit value. If MACSR[S/U] = 0 and MACSR[R/T] = 1, the
low-order 8 bits are used to round the resulting 32-bit fraction. If MACSR[S/U] = 1, the low-order
24 bits are used to round the resulting 16-bit fraction.
3 N Negative flag. Set if the msb of the result is set, otherwise cleared. N is affected only by MAC, MSAC,
and load operations; it is not affected by MULS and MULU instructions.
2 Z Zero flag. Set if the result equals zero, otherwise cleared. This bit is affected only by MAC, MSAC,
and load operations; it is not affected by MULS and MULU instructions.
1 V Overflow flag. Set if an arithmetic overflow occurs on a MAC or MSAC instruction indicating that the
result cannot be represented in the limited width of the EMAC. V is set only if a product overflow
occurs or the accumulation overflows the 48-bit structure. V is evaluated on each MAC or MSAC
operation and uses the appropriate PAVx flag in the next-state V evaluation.
0 EV Extension overflow flag. Signals that the last MAC or MSAC instruction overflowed the 32 lsbs in
integer mode or the 40 lsbs in fractional mode of the destination accumulator. However, the result is
still accurately represented in the combined 48-bit accumulator structure. Although an overflow has
occurred, the correct result, sign, and magnitude are contained in the 48-bit accumulator.
Subsequent MAC or MSAC operations may return the accumulator to a valid 32/40-bit result.

Table 4-1. MACSR Field Descriptions (Continued)

Bits Name Description