Zilog Z16F2810 Bedienungsanleitung PDF herunterladen (Seite 25)

UM018809-0611 Architectural Overview

ZNEO

CPU Core

User Manual

Program Counter Overflow Register

The Program Counter Overflow Register (PCOV) implements program counter overflow

protection. For more details, see the Program Counter Overflow

section on page 50.

Stack Pointer Overflow

The Stack Pointer Overflow Register (SPOV) is used to provide stack pointer overflow

protection. For more details, see the Stack Overflow

section on page 50. CALL, ILL,

IRET, POP, PUSH, RET and TRAP instructions, system interrupts and exceptions use the

ALU Register. R15 is used as the Stack Pointer.

Flags Register (FLAGS)

This byte register contains the status information regarding the most recent arithmetic,

logical, bit manipulation or rotate and shift operation. The Flags Register contains six bits

of status information that are set or cleared by CPU operations. Five of the bits (C, Z, S, V

and B) can be tested with conditional jump instructions. The

IRQE bit is the Master Inter-

rupt Enable flag, and the CIRQE bit is the Chained Interrupt Enable flag. Figure 2 displays

the flags and their bit positions in the Flags Register.

Interrupts, System Exceptions, and the software Trap (TRAP) instruction write the value

of the Flags Register to the stack. Executing an Interrupt Return (IRET) instruction

restores the value saved on the stack into the Flags Register.

Figure 2. Flags Register

CZSVBF1 CIRQE IRQE Flags Register

Bit

Master Interrupt Enable

Chained Interrupt Enable

User Flag 1

Blank Flag

Overflow Flag

Sign Flag

Zero Flag

Carry Flag

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