UM0438 datasheet(23/50 Pages) STMICROELECTRONICS

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UM0438

Simplified mnemonics for VLE instructions

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A.2.2

Subtract

Subtract from instructions subtract the second operand (rA) from the third (rB). The

simplified mnemonics in Table 11 use the more common order in which the third operand is

subtracted from the second.

A.3

Rotate and shift simplified mnemonics

Rotate and shift instructions provide powerful, general ways to manipulate register contents,

but they can be difficult to understand. Simplified mnemonics are provided for the following

operations:

●

Extract—Select a field of n bits starting at bit position b in the source register; left or

right justify this field in the target register; clear all other bits of the target register.

●

Insert—Select a left- or right-justified field of n bits in the source register; insert this

field starting at bit position b of the target register; leave other bits of the target register

unchanged.

●

Rotate—Rotate the contents of a register right or left n bits without masking.

●

Shift—Shift the contents of a register right or left n bits, clearing vacated bits (logical

shift).

●

Clear—Clear the leftmost or rightmost n bits of a register.

●

Clear left and shift left—Clear the leftmost b bits of a register, then shift the register left

by n bits. This operation can be used to scale a (known non-negative) array index by

the width of an element.

Table 10.

Subtract immediate simplified mnemonics

Simplified mnemonic

Standard mnemonic

e_sub16i rD,rA,value

e_add16i rD,rA,–value

e_sub2i. rA,value

e_add2i. rA,–value

e_sub2is rA,value

e_add2is rA,–value

e_subi rD,rA,value

e_addi rD,rA,–value

e_subic rD,rA,value

e_addic rD,rA,–value

e_subic. rD,rA,value

e_addic. rD,rA,–value

Table 11.

Subtract simplified mnemonics

Simplified mnemonic

Standard mnemonic(1)

rD,rB,rA is not the standard order for the operands. The order of rB and rA is reversed to show the

equivalent behavior of the simplified mnemonic.

sub[o][.] rD,rA,rB

subf[o][.] rD,rB,rA

subc[o][.] rD,rA,rB

subfc[o][.] rD,rB,rA

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