Samsung S3F80JB manual Register Addressing, Bit Register Pair

S3F80JB ADDRESS SPACES

REGISTER ADDRESSING

The S3C8-series register architecture provides an efficient method of working register addressing that takes full advantage of shorter instruction formats to reduce execution time.

With Register (R) addressing mode, in which the operand value is the content of a specific register or register pair, you can access all locations in the register file except for set 2. With working register addressing, you use a register pointer to specify an 8-byte working register space in the register file and an 8-bit register within that space.

Registers are addressed either as a single 8-bit register or as a paired 16-bit register space. In a 16-bit register pair, the address of the first 8-bit register is always an even number and the address of the next register is always an odd number. The most significant byte of the 16-bit data is always stored in the even-numbered register; the least significant byte is always stored in the next (+ 1) odd-numbered register.

Working register addressing differs from Register addressing because it uses a register pointer to identify a specific 8-byte working register space in the internal register file and a specific 8-bit register within that space.

MSB LSB

Rn Rn+1

n = Even address

Figure 2-9. 16-Bit Register Pair

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