HD404374FT datasheet(32/161 Pages) RENESAS

32 / 161 page

HD404374/HD404384/HD404389/HD404082/HD404084 Series

Rev.5.00, Sep.11.2003, page 32 of 161

W register (W), X register (X) and Y register (Y):

The W register is a 2-bit register, and the X and Y registers are 4-bit registers, used for RAM register

indirect addressing. The Y register is also used for D port addressing.

SPX register (SPX) and SPY register (SPY):

The SPX and SPY registers are 4-bit registers used as X register and Y register auxiliary registers,

respectively.

Carry flag (CA):

This flag holds ALU overflow when an arithmetic/logic instruction is executed. It is also affected by the

SEC, REC, ROTL, and ROTR instructions. The contents of the carry flag are saved to the stack when

interrupt handling is performed, and are restored from the stack by the RTNI instruction (but are not

affected by the RTN instruction).

Status flag (ST):

This flag holds ALU overflow when an arithmetic/logic or compare instruction is executed, and the result

of an ALU non-zero or bit test instruction. It is used as the branch condition for the BR, BRL, CAL, and

CALL instructions. The status flag is a latch-type flag, and does not change until the next arithmetic/logic,

compare, or bit test instruction is executed. After a BR, BRL, CAL, or CALL instruction, the status flag is

set to 1 regardless of whether the instruction is executed or skipped. The contents of the status flag are

saved to the stack when interrupt handling is performed, and are restored from the stack by the RTNI

instruction (but are not affected by the RTN instruction).

Program counter (PC):

This is a 14-bit binary counter that holds ROM address information.

Stack pointer (SP):

The stack pointer is a 10-bit register that holds the address of the next save space in the stack area. The

stack pointer is initialized to $3FF by an MCU reset. The stack pointer is decremented by 4 each time data

is saved, and incremented by 4 each time data is restored. The upper 4 bits of the stack pointer are fixed at

1111, so that a maximum of 16 stack levels can be used.

There are two ways in which the stack pointer is initialized to $3FF: by an MCU reset as mentioned above,

or by resetting the RSP bit with the REM or REMD instruction.

Reset

An MCU reset is performed by driving the

RESET pin low. At power-on, and when subactive mode,

watch mode, or stop mode is cleared,

RESET should be input for at least tRC to provide the oscillation

settling time for the oscillator.In other cases, the MCU is reset by inputting

RESET for at least two

instruction cycles.

Table 1 shows the areas initialized by an MCU reset, and their initial values.

HD404374FT Datasheet(PDF) 32 Page - Renesas Technology Corp