W79E804A/803A/802A
6.6 Data Pointers
The data pointers of W79E804 series are same as 8052 that has dual 16-bit Data Pointers (DPTR) by
setting DPS bit at AUXR1.0. The figure of dual DPTR is as below diagram.
DPS=0
DPTR
AUXR1.0
DPS
DPS=1
DPTR1
Figure 6-1: Dual DPTR
6.7 Architecture
The W79E804 series are based on the standard 8052 device. It is built around an 8-bit ALU that uses
internal registers for temporary storage and control of the peripheral devices. It can execute the
standard 8052 instruction set.
6.7.1 ALU
The ALU is the heart of the W79E804 series. It is responsible for the arithmetic and logical functions. It
is also used in decision making, in case of jump instructions, and is also used in calculating jump
addresses. The user cannot directly use the ALU, but the Instruction Decoder reads the op-code,
decodes it, and sequences the data through the ALU and its associated registers to generate the
required result. The ALU mainly uses the ACC which is a special function register (SFR) on the chip.
Another SFR, namely B register is also used in Multiply and Divide instructions. The ALU generates
several status signals which are stored in the Program Status Word register (PSW).
6.7.2 Accumulator
The Accumulator (ACC) is the primary register used in arithmetic, logical and data transfer operations
in the W79E804 series. Since the Accumulator is directly accessible by the CPU, most of the high
speed instructions make use of the ACC as one argument.
6.7.3 B Register
This is an 8-bit register that is used as the second argument in the MUL and DIV instructions. For all
other instructions it can be used simply as a general purpose register.
6.7.4 Program Status Word:
This is an 8-bit SFR that is used to store the status bits of the ALU. It holds the Carry flag, the Auxiliary
Carry flag, General purpose flags, the Register Bank Select, the Overflow flag, and the Parity flag.
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