Samsung S3C84E5 Using the Register Pointers, Programming TIP Setting the Register Pointers, SRP1

ADDRESS SPACES S3C84E5/C84E9/P84E9

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, RP# 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, it is recommended 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 either of the two 8-byte slices in the working register block, you can flexibly define the working register area to support program requirements.

FPROGRAMMING TIP — Setting the Register Pointers

SRP	#70H	;	RP0 ← 70H, RP1 ← 78H
SRP1	#48H	;	RP0 ← no change, RP1 ← 48H,
SRP0	#0A0H	;	RP0 ← 0A0H, RP1 ← no change
CLR	RP0	;	RP0 ← 00H, RP1 ← no change
LD	RP1,#0F8H	;	RP0 ← no change, RP1 ← 0F8H
		Register File
		Contains 32
		8-Byte Slices
0 0 0 0 1 X X X
RP1			FH (R15)
			8-Byte Slice	16-Byte Contiguous
			8H	Working Register
			7H
				block
0 0 0 0 0 X X X			8-Byte Slice
			0H (R0)
RP0
	Figure 2-6. Contiguous 16-Byte Working Register Block

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