Samsung S3F80JB manual Using the Register Pointers, Programming TIP Setting the Register Pointers

S3F80JB ADDRESS SPACES

USING THE REGISTER POINTERS

Register pointers RP0 and RP1, mapped to addresses D6H and D7H in set 1, are used to select two movable

8-byte working register slices in the register file. After a reset, they point to the working register common area: RP0 points to addresses C0H–C7H, and RP1 points to addresses C8H–CFH.

To change a register pointer value, you load a new value to RP0 and/or RP1 using an SRP or LD instruction (see Figures 2-6 and 2-7).

With working register addressing, you can only access those two 8-bit slices of the register file that are currently pointed to by RP0 and RP1. You cannot, however, use the register pointers to select a working register space in set 2, C0H–FFH, because these locations can be accessed only using the Indirect Register or Indexed addressing modes.

The selected 16-byte working register block usually consists of two contiguous 8-byte slices. As a general programming guideline, we recommend that RP0 point to the "lower" slice and RP1 point to the "upper" slice (see Figure 2-6). In some cases, it may be necessary to define working register areas in different (non-contiguous) areas of the register file. In Figure 2-7, RP0 points to the "upper" slice and RP1 to the "lower" slice.

Because a register pointer can point to the either of the two 8-byte slices in the working register block, you can define the working register area very flexibly to support program requirements.

PROGRAMMING TIP — Setting the Register Pointers

SRP	#70H	;	RP0 ← 70H, RP1 ← 78H
SRP1	#48H	;	RP0 ← no change, RP1 ← 48H,
SRP0	#0A0H	;	RP0 ← A0H, RP1 ← no change
CLR	RP0	;	RP0 ← 00H, RP1 ← no change
LD	RP1,#0F8H	;	RP0 ← no change, RP1 ← 0F8H

0 0 0 0 1 X X X

RP1

0 0 0 0 0 X X X

RP0

Register File

Contains 32

8-Byte Slices

8-Byte Slice

8-Byte Slice

0FH (R15)

08H

07H

00H (R0)

16-byte contiguous working register block

Figure 2-7. Contiguous 16-Byte Working Register Block

2-11