* bit6 - VF - Overflow Flag: 1 on signed overflow
* bit5 - Unused: always set to 1
* bit4 - BF - Break Command Flag: 1 when interrupt was caused pushed by instructions (BRK/ PHP) and 0 when pushed by interrupts (NMI / IRQ)
* bit3 - DF - Decimal Mode Flag: 1 when CPU is in Decimal Mode
* bit2 - IF - Interrupt Disable Flag: when 1, no interrupt will occur (except BRK and NMI)