Zilog Z16F2810 - Manual (Page 25)

UM018809-0611 Architectural Overview
ZNEO
®
CPU Core
User Manual
9
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
C Z S V B F1 CIRQE IRQE Flags Register
Bit
0
Bit
7
Master Interrupt Enable
Chained Interrupt Enable
User Flag 1
Blank Flag
Overflow Flag
Sign Flag
Zero Flag
Carry Flag