Maxim Integrated High-Speed Microcontroller Users Guide: DS80C390 Supplement - Manual (Page 66)

High-Speed Microcontroller User’s Guide: DS80C390 Supplement
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MULTIPLIER CONTROL REGISTER ZERO (MCNT0)
7 6 5 4 3 2 1 0
SFR D1h LSHIFT CSE SCE MAS4 MAS3 MAS2 MAS1 MAS0
RW-0 RW-0 RW-0 RW-0 RW-0 RW-0 RW-0 RW-0
R = Unrestricted Read, W = Unrestricted Read, -n = Value after Reset
LSHIFT
Bit 7
Left Shift. This bit works in conjunction with the SCE and CSE bits to
determine the direction and path of arithmetic accelerator shift operations as
shown below. When LSHIFT =0, shift operations will shift from the LSb to the
MSb, and vice versa when LSHIFT =1. LSHIFT does not alter any other type of
calculation other than the shift function. The LSHIFT bit is cleared to 0 following
a either a system reset or the initialization of the accelerator.
CSE
Bit 6 Circular Shift Enable. This bit works in conjunction with the SCE and LSHIFT
bits to determine the direction and path of arithmetic accelerator shift operations
as shown below. When CSE=1, shifts of the arithmetic accelerator will wrap bit
31 to bit 0 or vice versa depending on the settings of the LSHIFT bits. When
CSE is cleared to a 0, all left or right shifts will shift cleared bit values into the
most significant bit for a right shift and the least significant bit for a left shift.
When CSE is set to a 1 and SCB is set to a 1, the most significant bit will be
shifted into the 32 Bit Carry Bit when doing a left shift and least most significant
bit will be shifted into the 32 Bit Carry Bit when doing a right shift. The CSE bit
is cleared to 0 following a system reset.
SCE
Bit 5 Shift Carry Enable. This bit works in conjunction with the CSE and LSHIFT
bits to determine the direction and path of arithmetic accelerator shift operations
as shown below. When SCE=1 the arithmetic accelerator carry bit will be shifted
into the LSb for a left shift and into the MSb for a right shift. When SCE=0, shifts
will not incorporate the arithmetic accelerator carry bit as a part of the shifting
process. If CSE=0 the arithmetic accelerator carry bit will remain unchanged
during the shift process. If CSE=1 the MSb will be shifted into the carry bit on a
left shift and the least most significant bit of the arithmetic accelerator will be
shifted into the carry bit on a right shift. The SCE bit is cleared to 0 following a
system reset.
Arithmetic Accelerator Values After Shift
SCE CSE LSHIFT MSb (bit 31) LSb (bit 0) Carry bit
0 0 0 Previous bit 30 Previous bit 0 unchanged
0 0 1 0 Previous bit 1 unchanged
0 1 0 Previous bit 30 Previous bit 31 unchanged
0 1 1 Previous bit 0 Previous bit 1 unchanged
1 0 0 Previous bit 30 Previous carry unchanged
1 0 1 Previous carry Previous bit 1 unchanged
1 1 0 Previous bit 30 Previous carry Previous bit 31
1 1 1 Previous carry Previous bit 1 Previous bit 0