Samsung S3F80JB manual Bit Working Register Addressing

S3F80JB 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 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).

These address bits indicate

8-bit working register addressing

RP0

RP1

	Selects
	RP0 or RP1
						Address
								8-bit logical
		1	1	0	0
								address
							Three low-
Register pointer							order bits
provides five
high-order bits

8-bit physical address

Figure 2-14. 8-Bit Working Register Addressing

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