NEC V30MZ flags: Difference between revisions
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| |||| || | +--- Parity (PF<sup>P</sup>) | | |||| || | +--- Parity (PF<sup>P</sup>) | ||
| |||| || +------ Auxillary Carry (AF<sup>AC</sup>) | | |||| || +------ Auxillary Carry (AF<sup>AC</sup>) | ||
| |||| |+-------- Zero (Z) | | |||| |+-------- Zero (ZF<sup>Z</sup>) | ||
| |||| +--------- Sign (S) | | |||| +--------- Sign (SF<sup>S</sup>) | ||
| |||+------------ Single Step<sup>Break</sup> (TF<sup>BRK</sup>) | | |||+------------ Single Step<sup>Break</sup> (TF<sup>BRK</sup>) | ||
| ||+------------- Interrupt Enable (IF<sup>IE</sup>) | | ||+------------- Interrupt Enable (IF<sup>IE</sup>) | ||
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The following flags are typically modified by the developer: | The following flags are typically modified by the developer: | ||
{{Anchor|TF}} | |||
=== Single step === | === Single step === | ||
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Alternatively referred to as the ''trap flag''. | Alternatively referred to as the ''trap flag''. | ||
{{Anchor|IF}} | |||
=== Interrupt enable === | === 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}} | |||
=== Direction === | === 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}} | |||
=== Mode === | === 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. | ||
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 (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:
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.
