When the interrupt receives the signal, the processor comes to action and saves the contents of the PC register. It saves it in the stack and branches to the 24h address that conveys the idea of hexadecimal. The distinct feature of all maskable interrupts is that they can be enabled or disabled by the use of EI and DI instructions. When it comes to the RST 5.5, RST 6.5 and RST 7.5 interrupts, they can be made enabled or disabled individually by the use of the SIM instruction.
These are hardware interrupts. When any Interrupt is executed then microprocessor stops working what its doing and starts to execute the interrupt. RST means Restart. 4.5,5.5,6.5,7.5 all these value shows the address. When RST 4.5 executes then microprocessor starts to execute the program from 0024 H(hexadecimal) as 4.5 means 4.5*8 = 36 in decimal.
When you convert it into hexadecimal then it is 24 H. Rst 4.5 is also known as TRAP. It is non-maskable and has the highest priority among all other hardware interrupts. So for power failure you should give interrupt on this pin(pin no 6). RST 5.5,6.5,7.5 are maskable interrupts. They can be enabled or disabled by using the EI(Enable Interrupt) and DI instruction.
You can also check the the status of pending and masking of these interrupts by using the RIM(Read Interrupt Masking) instruction.