NEC V30MZ flags: Difference between revisions
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{{Anchor|CF}} | {{Anchor|CF}} | ||
=== Carry === | === CF - 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}} | {{Anchor|PF}} | ||
=== Parity === | === PF - 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}} | {{Anchor|AF}} | ||
=== Auxillary Carry === | === AF - 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}} | {{Anchor|ZF}} | ||
=== Zero === | === ZF - 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}} | {{Anchor|SF}} | ||
=== Sign === | === SF - 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}} | {{Anchor|OF}} | ||
=== Overflow === | === OF - Overflow === | ||
Set to <tt>1</tt> if an overflow occured as part of the arithmetic operation. | Set to <tt>1</tt> if an overflow occured as part of the arithmetic operation. | ||
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{{Anchor|TF}} | {{Anchor|TF}} | ||
=== Single step === | === TF - Single step === | ||
If set to <tt>1</tt>, after every instruction, a software interrupt (vector 1) is generated. | If set to <tt>1</tt>, after every instruction, a software interrupt (vector 1) is generated. | ||
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{{Anchor|IF}} | {{Anchor|IF}} | ||
=== Interrupt enable === | === IF - Interrupt enable === | ||
If set to <tt>1</tt>, enables maskable interrupt handling via the interrupt vector table; cleared to <tt>0</tt> as part of interrupt handling and restored by the <tt>IRET</tt> opcode. | If set to <tt>1</tt>, enables maskable interrupt handling via the interrupt vector table; cleared to <tt>0</tt> as part of interrupt handling and restored by the <tt>IRET</tt> opcode. | ||
{{Anchor|DF}} | {{Anchor|DF}} | ||
=== Direction === | === DF - Direction === | ||
If set to <tt>1</tt>, string instructions decrement pointers as part of their operation; if set to <tt>0</tt>, the pointers are to be incremented. | If set to <tt>1</tt>, string instructions decrement pointers as part of their operation; if set to <tt>0</tt>, the pointers are to be incremented. | ||
{{Anchor|MD}} | {{Anchor|MD}} | ||
=== Mode === | === MD - 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. | 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. | ||
Latest revision as of 11:04, 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 (ZFZ) | |||| +--------- Sign (SFS) | |||+------------ Single StepBreak (TFBRK) | ||+------------- Interrupt Enable (IFIE) | |+-------------- Direction (DFDIR) | +--------------- Overflow (OFV) +-------------------- Mode (MD)
Status flags
The following flags are typically modified by instructions:
CF - Carry
Stores the carry/borrow state of the last arithmetic operation, or the bit shifted to it for shift/rotate operations.
PF - Parity
Set to 1 if, after arithmetic and logical operations, the lower 8 bits of the result are even.
AF - 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.
ZF - Zero
Set to 1 if, after arithmetic and logical operations, the result is equal to zero.
SF - Sign
Set to 1 if, after arithmetic and logical operations, the highest bit of the result is set.
OF - 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:
TF - Single step
If set to 1, after every instruction, a software interrupt (vector 1) is generated.
Alternatively referred to as the trap flag.
IF - 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.
DF - Direction
If set to 1, string instructions decrement pointers as part of their operation; if set to 0, the pointers are to be incremented.
MD - 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.
