Maxim Integrated High-Speed Microcontroller Users Guide: DS80C390 Supplement - Manual (Page 156)

High-Speed Microcontroller User’s Guide: DS80C390 Supplement
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SECTION 20: ARITHMETIC ACCELERATOR
(DS80C390 Supplement Only)
The DS80C390 incorporates an arithmetic accelerator that performs 32- and 16-bit calculations while
maintaining 8051 software compatibility. Math operations are performed by sequentially loading three
special registers. The mathematical operation is determined by the sequence in which three dedicated
SFRs (MA, MB, and MCNT0) are accessed, eliminating the need for a special step to choose the
operation. The arithmetic accelerator has four functions: multiply, divide, shift right/left, and normalize.
The normalize function facilitates the conversion of 4-byte unsigned binary integers into floating point
format. An integral 40-bit accumulator, described later, supports multiply-and-add and divide-and-add
operations. The following table shows the operations supported by the math accelerator and their time of
execution.
Table 20-1.
ARITHMETIC ACCELERATOR EXECUTION TIMES
OPERATION RESULT EXECUTION TIME
32-bit/16-bit divide 32-bit quotient, 16-bit remainder 36 t
CLCL
16-bit/16-bit divide 16-bit quotient, 16-bit remainder 24 t
CLCL
16-bit/16-bit multiply 32-bit product 24 t
CLCL
32-bit shift left/right 32-bit result 36 t
CLCL
32-bit normalize 32-bit mantissa, 5 bit exponent 36 t
CLCL
The following is a brief summary of the bits and registers used in conjunction with arithmetic acceleration
operations. Please consult the SFR listing in Section 4for a complete description of all these registers.
LSHIFT
MCNT0.7
Left Shift. This bit determines whether shift operations proceed from LSb to MSb or
vice versa.
CSE
MCNT0.6 Circular Shift Enable. This bit determines whether shift operations will wrap between
the LSb and MSb.
SCE
MCNT0.5 Shift Carry Enable. This bit determines whether the arithmetic accelerator carry bit is
included in the shift process.
MAS4-0
MCNT0.4-0. Multiplier Register Shift Bits. When performing a shift operation, these bits
determine how many shifts to perform. Following a normalize operation, these bits will
contain indicate the number shifts performed.
MST
MCNT1.7 Multiply/Accumulate Status Flag. This bit serves as a busy flag for the arithmetic
accumulator operations.
MOF
MCNT1.6 Multiply Overflow Flag. This bit is set when a divide-by-0 or when the result of a
calculation exceeds FFFFh.
SCB
MCNT1.5 Shift Carry Bit. This bit serves as the carry bit during arithmetic accelerator shift
operations when SCE=1. This bit must be cleared (or set) by software as desired before
each new shift operation.
CLM
MCNT1.4 Clear Accelerator Registers. Setting this bit clears the MA, MB, and MC registers.
MA
MA.7-0 Multiplier A Register. This register is used as both a source and result register for
various arithmetic accelerator functions.
MB
MB.7-0 Multiplier B Register. This register is used as both a source and result register for
various arithmetic accelerator functions.
MC
MC.7-0 Multiplier C Register. This register serves as the 40-bit accumulator of the arithmetic
accelerator.