Control of the 8051 ports through software is carried out using what
are known as ‘special function registers’ (SFRs).
Physically, the SFR is a area of memory in internal RAM:
• P0 is at address 0x80
• P1 at address 0x90
• P2 at address 0xA0
• P3 at address 0xB0
NOTE: 0x means that the number format is HEXADECIMAL
