Samsung S3C84E5 user manual Register Addressing, Bit Register Pair

ADDRESS SPACES S3C84E5/C84E9/P84E9

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 any location 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, and the least significant byte is always stored in the next (+1) odd-numbered register.

Working register addressing differs from Register addressing as 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 2-8. 16-Bit Register Pair

2-12