PM0214 datasheet(60/245 Pages) STMICROELECTRONICS

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The STM32 Cortex-M4 instruction set

PM0214

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DocID022708 Rev 4

Constant

You specify an operand2 constant in the form #constant, where constant can be:

•

Any constant that can be produced by shifting an 8-bit value left by any number of bits

within a 32-bit word.

•

Any constant of the form 0x00XY00XY

•

Any constant of the form 0xXY00XY00

•

Any constant of the form 0xXYXYXYXY

In the constants shown above, X and Y are hexadecimal digits.

In addition, in a small number of instructions, constant can take a wider range of values.

These are described in the individual instruction descriptions.

When an operand2 constant is used with the instructions MOVS, MVNS, ANDS, ORRS,

ORNS, EORS, BICS, TEQ or TST, the carry flag is updated to bit[31] of the constant, if the

constant is greater than 255 and can be produced by shifting an 8-bit value. These

instructions do not affect the carry flag if operand2 is any other constant.

Instruction substitution

Your assembler might be able to produce an equivalent instruction in cases where you

specify a constant that is not permitted. For example, an assembler might assemble the

instruction CMP Rd, #0xFFFFFFFE as the equivalent instruction CMN Rd, #0x2.

An operand2 register is specified in the form Rm {, shift}, where:

•

Rm is the register holding the data for the second operand

•

Shift is an optional shift to be applied to Rm. It can be one of:

ASR #n: Arithmetic shift right n bits, 1

≤n ≤32

LSL #n: Logical shift left n bits, 1

≤n ≤31

LSR #n: Logical shift right n bits, 1

≤n ≤32

ROR #n: Rotate right n bits, 1

≤n ≤31

RRX: Rotate right one bit, with extend

—: If omitted, no shift occurs, equivalent to LSL #0

If you omit the shift, or specify LSL #0, the instruction uses the value in Rm.

If you specify a shift, the shift is applied to the value in Rm, and the resulting 32-bit value is

used by the instruction. However, the contents in the register Rm remains unchanged.

Specifying a register with shift also updates the carry flag when used with certain

instructions. For information on the shift operations and how they affect the carry flag, see

Shift operations.

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