cessing, not during
regular program execution, and is used to determine whether an interrupt
comes from a break instruction or from a hardware interrupt. The 65816
Native mode P Register does not have a B flag; instead it has a dedicated
break vector ($00FFE6-00FFE7).

THE 65816 P REGISTER

The 65816 uses all eight bits in the P Register. Bit 0 includes what is
called a "phantom" bit and is used for switching from Emulation to Native
mode and back. I will fully explain this phantom emulation bit next time
out.

65816 Status Register Bit-fields

Bit 7 6 5 4 3 2 1 0
N V m x D I Z C/e

The m and x bits reflect the size of data used in the A Register and X/Y
index registers, respectively. The x bit affects both the X and Y
registers.

THE PROGRAM COUNTER (PC)

The final register in our list is the program counter, or PC. It is a
16-bit register that holds the address of the next instruction to be
executed. The program counter is normally incremented to point to the next instruction in memory, except in the case of jump, branch, and call instructions, which pass control to a new location within the program by storing the new location to the program counter. If the program counter
goes past $FFFF it wraps around to $0000.

IN CONCLUSION

Today was all about 6502/65816 architecture, with a couple of short
paragraphs on the 65x family's early days. I sincerely hope this was informative yet not too "techy", and look forward to next time when we will discuss numbering systems used by 6502 assembly language programmers, as
well as introducing the Native mode of the 65816. So, until our next
meeting, take 'er easy.

Please send errors, omissions, or suggestions to bert@winc64.com or on
Lemon64, username satpro.

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