PM0056 datasheet(89/156 Pages) STMICROELECTRONICS

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PM0056

The Cortex-M3 instruction set

3.8.1

BFC and BFI

Bit Field Clear and Bit Field Insert.

Syntax

BFC{cond} Rd, #lsb, #width

BFI{cond} Rd, Rn, #lsb, #width

where:

•

‘cond’ is an optional condition code, see Conditional execution on page 57.

•

‘Rd’ is the destination register.

•

‘Rn’ is the source register.

•

‘lsb’ is the position of the least significant bit of the bitfield. lsb must be in the range 0 to

31.

•

‘width’ is the width of the bitfield and must be in the range 1 to 32-lsb.

Operation

BFC clears a bitfield in a register. It clears width bits in Rd, starting at the low bit position lsb.

Other bits in Rd are unchanged.

BFI copies a bitfield into one register from another register. It replaces width bits in Rd

starting at the low bit position lsb, with width bits from Rn starting at bit[0]. Other bits in Rd

are unchanged.

Restrictions

Do not use SP and do not use PC.

Condition flags

These instructions do not affect the flags.

Examples

BFC

R4, #8, #12

; Clear bit 8 to bit 19 (12 bits) of R4 to 0

BFI

R9, R2, #8, #12

; Replace bit 8 to bit 19 (12 bits) of R9 with

; bit 0 to bit 11 from R2

3.8.2

SBFX and UBFX

Signed Bit Field Extract and Unsigned Bit Field Extract.

Syntax

SBFX{cond} Rd, Rn, #lsb, #width

UBFX{cond} Rd, Rn, #lsb, #width

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