CPU Registers
3-8 RISC 16-Bit CPU
3.2.5 GeneralPurpose Registers R4 - R15

The twelve registers, R4R15, are general-purpose registers. All of these

registers can be used as data registers, address pointers, or index values and

can be accessed with byte or word instructions as shown in Figure 37.

Figure 37. Register-Byte/Byte-Register Operations
Unused
High Byte Low Byte
Byte
Register-Byte Operation
0h
High Byte Low Byte
Byte
Byte-Register Operation
Register
Memory Register
Memory
Example Register-Byte Operation Example Byte-Register Operation
R5 = 0A28Fh R5 = 01202h
R6 = 0203h R6 = 0223h
Mem(0203h) = 012h Mem(0223h) = 05Fh
ADD.B R5,0(R6) ADD.B @R6,R5
08Fh 05Fh
+ 012h + 002h
0A1h 00061h
Mem (0203h) = 0A1h R5 = 00061h
C = 0, Z = 0, N = 1 C = 0, Z = 0, N = 0
(Low byte of register) (Addressed byte)
+ (Addressed byte) + (Low byte of register)
>(Addressed byte) >(Low byte of register, zero to High byte)