dsp56800e Freescale Semiconductor, Inc, dsp56800e Datasheet - Page 64

• Manufacturer Part Number: dsp56800e
• Description: 16-bit Digital Signal Controller Core
• Manufacturer: Freescale Semiconductor, Inc

Data Types and Addressing Modes
When a MOVE.W or MOVE.L instruction is used to write an accumulator extension register to memory,
the value is sign extended to 16 or 32 bits before it is written.
3.4.2
The alignment of data within the 16-bit data registers is shown in Figure 3-5. Moves of words (MOVE.W)
from memory (integer or fractional) fill the entire 16-bit register. Signed moves of bytes from memory
(MOVE.B or MOVE.BP) are put in the lower 8 bits of the data register and are sign extended in the upper
8 bits. Unsigned moves are marked with “U” (MOVEU.B or MOVEU.BP) and place zero extension into
the upper 8 bits of the data register.
The Y register, the combination of the Y0 and Y1 registers, can hold a full 32-bit value. It is always read or
written with a long-word move instruction (MOVE.L), and it is never sign extended or zero extended
because a 32-bit value completely fills it.
3.4.3
The 24-bit registers in the AGU include the address pointer registers (R0–R5, N, and SP), loop address
registers (LA and LA2), and the hardware stack register (HWS). All values (byte, word, and long word) are
right aligned in the destination register. When an unsigned move instruction is used to load one of these
registers, the value is zero extended to the full register width. Signed moves cause the value to be sign
extended. The placement of data in AGU registers from memory appears in Figure 3-6 on page 3-15.
3-14
Data Alignment in Data Registers
Data Alignment in 24-Bit AGU and Control Registers
MOVE.B
MOVE.BP
MOVE.W
MOVE.W
MOVE.L
Figure 3-5. Supported Data Types in Data Registers (X0, Y1, Y0)
Example 3-5. Storing Accumulators with Different Data Types
A1,X:(R0+3)
A1,X:(R0)
A1,X:(R0)
A,X:(R0)
A10,X:(R0)
MOVE.B (Signed Byte Move)
MOVEU.B (Unsigned Byte Move)
MOVE.W (Signed Word Move)
DSP56800E Core Reference Manual
; store accumulator byte (no saturation)
; store accumulator byte (no saturation)
; store accumulator word (no saturation)
; store accumulator word (saturation)
; store accumulator long (no saturation)
15
15
15
Extension
Extension
Sign
Zero
8 7
8 7
0
0
0
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