8085中发现的b/w栈指针和w - z寄存器有什么区别?

I am bit confused with the functionality of Stack Pointer and W-Z Registers present in 8085 microprocessor.A stack pointer is used to store the address during a interrupt call which further load into the programme counter to continue execution of programme,but as i have read from book the W-Z also utilised for same functionality. I am bit confused with the functionality of Sta