Intel 80C196NU Accumulator Control and Status Register Accstat, Bit Function Number Mnemonic

ADVANCED MATH FEATURES

3.4ACCUMULATOR CONTROL AND STATUS REGISTER (ACC_STAT)

The ACC_STAT register controls the operating mode and reflects the status of the accumulator. The mode bits (FME and SME) are effective only for signed multiplication. Table 3-2 describes the 80C196NU’s operation with each of the four possible configurations of these bits.

ACC_STAT	Address:	0BH
(80C196NU)	Reset State:	00H

The accumulator control and status (ACC_STAT) register enables and disables fractional and saturation modes and contains three status flags that indicate the status of the accumulator’s contents.

80C196NU

7

FME SME — —

0

— STOVF OVF STSAT

Bit	Bit	Function
Number	Mnemonic
7	FME	Fractional Mode Enable
		Set this bit to enable fractional mode. (See Table 3-2.) In this mode, the
		result of a signed multiplication instruction is shifted left by one bit before it
		is added to the contents of the accumulator.
		For unsigned multiplication, this bit is ignored.
6	SME	Saturation Mode Enable
		Set this bit to enable saturation mode. (See Table 3-2.) In this mode, the
		result of a signed multiplication operation is not allowed to overflow or
		underflow.
		For unsigned multiplication, this bit is ignored.
5:3	—	Reserved; for compatibility with future devices, write zeros to these bits.
2	STOVF	Sticky Overflow Flag
		For unsigned multiplication, this bit is set if a carry out of bit 31 occurs.
		Unless saturation mode is enabled, this bit is set for signed multiplication to
		indicate that the sign bit of the accumulator and the sign bit of the addend
		are equal, but the sign bit of the result is the opposite. (See Table 3-2.)
		Software can clear this flag; hardware does not clear it.
1	OVF	Overflow Flag
		This bit indicates that an overflow occurred during the preceding accumu-
		lation. (See Table 3-2.)
		This flag is dynamic; it can change after each accumulation.
0	STSAT	Sticky Saturation Flag
		This bit indicates that a saturation has occurred during accumulation with
		saturation mode enabled. (See Table 3-2.)
		Software can clear this flag; hardware does not clear it.

Figure 3-2. Accumulator Control and Status (ACC_STAT) Register

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