Product data

HD404818 Series

Functional Description

Registers and Flags

The MCU provides ten registers and two flags for CPU operations. They are illustrated in figure 5 and

described in the following paragraphs.

(B)

(A)

(W)

(X)

(Y)

(SPX)

(SPY)

(CA)

(ST)

(PC)

(SP)

1111

Accumulator

B register

W register

X register

Y register

SPX register

SPY register

Carry

Status

Program counter

Initial value: 0,

no R/W

Stack pointer

Initial value: $3FF, no R/W

(V)

Initial value: Undefined, R/W

V register Initial value: 0, R/W

Initial value: Undefined, R/W

Initial value: 1, no R/W

Figure 5 Registers and Flags

Accumulator (A), B Register (B): The accumulator and B register are 4-bit registers which hold the

results of the arithmetic logic unit (ALU), and exchange data between memory, I/O, and other registers.