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CHAPTER 11 INTERRUPT FUNCTIONS

User’s Manual U12978EJ3V0UD

169

(4) Program status word (PSW)

The program status word is a register used to hold the instruction execution result and the current status for

interrupt requests. The IE flag to set maskable interrupt enable/disable is mapped here.

Besides 8-bit unit read/write, this register can carry out operations with bit manipulation instructions and

dedicated instructions (EI, DI). When a vectored interrupt is acknowledged, the PSW is automatically saved into

a stack, and the IE flag is reset to 0.

RESET input sets the PSW to 02H.

Figure 11-5. Configuration of Program Status Word

IE Z 0 AC 0 0 1 CYPSW

76543210

02H

Symbol

After reset

Used when normal instruction is executed

Interrupt acknowledgment enabled/disabled

Disabled

Enabled

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Nec switch Manual do Utilizador Página 169