NEC V30MZ flags: Difference between revisions
(Created page with " = NEC V30MZ flags = == Layout == The V30MZ processor features a 16-bit flag register: 15 bit 8 7 bit 0 ---- ---- ---- ---- m111 odit sz0a 0p1c | |||| || | | | | |||| || | | +- Carry (CF<sup>CY</sup>) | |||| || | +--- Parity (PF<sup>P</sup>) | |||| || +------ Auxillary Carry (AF<sup>AC</sup>) | |||| |+-------- Zero (Z) | |||| +--------- Sign (S) | |||+------------ Single Step<sup>Break</sup> (TF<sup>BRK</sup>)...") |
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The following flags are typically modified by instructions: | The following flags are typically modified by instructions: | ||
{{Anchor|CF}} | |||
=== Carry === | === Carry === | ||
Stores the carry/borrow state of the last arithmetic operation, or the bit shifted to it for shift/rotate operations. | Stores the carry/borrow state of the last arithmetic operation, or the bit shifted to it for shift/rotate operations. | ||
{{Anchor|PF}} | |||
=== Parity === | === Parity === | ||
Set to <tt>1</tt> if, after arithmetic and logical operations, the lower 8 bits of the result are even. | Set to <tt>1</tt> if, after arithmetic and logical operations, the lower 8 bits of the result are even. | ||
{{Anchor|AF}} | |||
=== Auxillary Carry === | === Auxillary Carry === | ||
Stores the carry state from the lower 4-bit nibble (bits 0-3) to the higher 4-bit nibble (bits 4-7), or the borrow state from the higher nibble to the lower nibble. | Stores the carry state from the lower 4-bit nibble (bits 0-3) to the higher 4-bit nibble (bits 4-7), or the borrow state from the higher nibble to the lower nibble. | ||
{{Anchor|ZF}} | |||
=== Zero === | === Zero === | ||
Set to <tt>1</tt> if, after arithmetic and logical operations, the result is equal to zero. | Set to <tt>1</tt> if, after arithmetic and logical operations, the result is equal to zero. | ||
{{Anchor|SF}} | |||
=== Sign === | === Sign === | ||
Set to <tt>1</tt> if, after arithmetic and logical operations, the highest bit of the result is set. | Set to <tt>1</tt> if, after arithmetic and logical operations, the highest bit of the result is set. | ||
{{Anchor|OF}} | |||
=== Overflow === | === Overflow === | ||
Revision as of 10:59, 28 December 2024
NEC V30MZ flags
Layout
The V30MZ processor features a 16-bit flag register:
15 bit 8 7 bit 0 ---- ---- ---- ---- m111 odit sz0a 0p1c | |||| || | | | | |||| || | | +- Carry (CFCY) | |||| || | +--- Parity (PFP) | |||| || +------ Auxillary Carry (AFAC) | |||| |+-------- Zero (Z) | |||| +--------- Sign (S) | |||+------------ Single StepBreak (TFBRK) | ||+------------- Interrupt Enable (IFIE) | |+-------------- Direction (DFDIR) | +--------------- Overflow (OFV) +-------------------- Mode (MD)
Status flags
The following flags are typically modified by instructions:
Carry
Stores the carry/borrow state of the last arithmetic operation, or the bit shifted to it for shift/rotate operations.
Parity
Set to 1 if, after arithmetic and logical operations, the lower 8 bits of the result are even.
Auxillary Carry
Stores the carry state from the lower 4-bit nibble (bits 0-3) to the higher 4-bit nibble (bits 4-7), or the borrow state from the higher nibble to the lower nibble.
Zero
Set to 1 if, after arithmetic and logical operations, the result is equal to zero.
Sign
Set to 1 if, after arithmetic and logical operations, the highest bit of the result is set.
Overflow
Set to 1 if an overflow occured as part of the arithmetic operation.
Control flags
The following flags are typically modified by the developer:
Single step
If set to 1, after every instruction, a software interrupt (vector 1) is generated.
Alternatively referred to as the trap flag.
Interrupt enable
If set to 1, enables maskable interrupt handling via the interrupt vector table; cleared to 0 as part of interrupt handling and restored by the IRET opcode.
Direction
If set to 1, string instructions decrement pointers as part of their operation; if set to 0, the pointers are to be incremented.
Mode
This flag does nothing on the NEC V30MZ. It was used to implement 8080 emulation mode in other V20/V30-family chips, but this functionality has been removed in the V30MZ.
