Encrypted Microprocessor PIC18F4458 Code Extraction is quite necessary and it is a final step for MCU cracking, the status of Microcontroller PIC18F4458 will be reset to unlocked one and program in the flash and data in the eeprom can be dump out;
A CALL type instruction causes a push onto the stack; the stack pointer is first incremented and the location pointed to by the stack pointer is written with the contents of the PC (already pointing to the instruction following the CALL). A RETURN type instruction causes a pop from the stack; the contents of the location pointed to by the STKPTR are transferred to the PC and then the stack pointer is decremented when extract code from atmega88v.
The stack pointer is initialized to ‘00000’ after all Resets. There is no RAM associated with the location corresponding to a stack pointer value of ‘00000’; this is only a Reset value. Status bits indicate if the stack is full or has overflowed or has underflowed. Only the top of the return address stack (TOS) is readable and writable. A set of three registers, TOSU:TOSH:TOSL, hold the contents of the stack location pointed to by the STKPTR register (Figure 5-2). This allows users to implement a software stack if necessary.
After aCALL, RCALL or interrupt, the software can read the pushed value by reading the TOSU:TOSH:TOSLregisters. These values can be placed on a user defined software stack. At return time, the software can returnthese values to TOSU:TOSH:TOSL and do a return. The user must disable the global interrupt enable bits while accessing the stack to prevent inadvertent stack corruption before the heximal of chip can be extracted.
The STKPTR register (Register 5-1) contains the stack pointer value, the STKFUL (stack full) status bit and the STKUNF (stack underflow) status bits. The value of the stack pointer can be 0 through 31. The stack pointerincrements before values are pushed onto the stack and decrements after values are popped off the stack.
On Reset, the stack pointer value will be zero. The user may read and write the stack pointer value. This feature can be used by a Real-Time Operating System (RTOS) for return stack maintenance.
After the PC is pushed onto the stack 31 times (without popping any values off the stack), the STKFUL bit is set. The STKFUL bit is cleared by software or by a POR.
