Samsung S3C84E5 user manual Bit Working Register Addressing

S3C84E5/C84E9/P84E9 ADDRESS SPACES

8-BIT WORKING REGISTER ADDRESSING

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 2-13, 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 2-14 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 3 ("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).

These address bits indicate 8-bit working register addressing

Selects

RP0 or RP1

Address

1 1 0 0

RP0

RP1

8-bit logical address

Register pointer	Three low-order bits
provides five
high-order bits

8-bit physical address

Figure 2-13. 8-Bit Working Register Addressing

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