Samsung C8278X ユーザーズマニュアル

You can also use 8-bit working register addressing to access registers in a selected working register area. To 
initiate 8-bit working register addressing, the upper four bits of the instruction address must contain the value 
"1100B." This 4-bit value (1100B) indicates that the remaining four bits have the same effect as 4-bit working 
register addressing. 

As shown in Figure 2-15, the lower nibble of the 8-bit address is concatenated in much the same way as for 4-bit 
addressing: Bit 3 selects either RP0 or RP1, which then supplies the five high-order bits of the final address; the 
three low-order bits of the complete address are provided by the original instruction. 

Figure 2-16 shows an example of 8-bit working register addressing. The four high-order bits of the instruction 
address (1100B) specify 8-bit working register addressing. Bit 4 ("1") selects RP1 and the five high-order bits in 
RP1 (10101B) become the five high-order bits of the register address. The three low-order bits of the register 
address (011) are provided by the three low-order bits of the 8-bit instruction address. The five address bits from 
RP1 and the three address bits from the instruction are concatenated to form the complete register address, 
0ABH (10101011B). 

8-bit logical
address

8-bit physical address

Register pointer
provides five
high-order bits

Address

Selects
RP0 or RP1

RP1

RP0

Three low-order bits

These address
bits indicate 8-bit
working register
addressing