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Read Microcontroller PIC18F442 Software out from its flash and eeprom memory, the status of MCU can be reset after cut off the security fuse bit by the laser and the first step is to decapsulate the Microcontroller in the process of IC breaking;

Read Microcontroller PIC18F442 Software out from its flash and eeprom memory, the status of MCU can be reset after cut off the security fuse bit by the laser and the first step is to decapsulate the Microcontroller

The top of the stack is readable and writable. Three register locations, TOSU, TOSH and TOSL hold the contents of the stack location pointed to by the STKPTR register. This allows users to implement a software stack if necessary.

After a CALL, RCALL or interrupt, the software can read the pushed value by reading the TOSU, TOSH and TOSL registers. These values can be placed on a user defined software stack.

At return time, the software can replace the TOSU, TOSH and TOSL and do a return. The user must disable the global interrupt enable bits during this time to prevent inadvertent stack operations.

The STKPTR register contains the stack pointer value, the STKFUL (stack full) status bit, and the STKUNF (stack underflow) status bits. Register 4-1 shows the STKPTR register. The value of the stack pointer can be 0 through 31. The stack pointer increments when values are pushed onto the stack and decrements when values are popped off the stack. At RESET, the stack pointer value will be deciphering Microcontroller.

The user may read and write the stack pointer value. This feature can be used by a Real Time Operating System 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 can only be cleared in software or by a POR.

The action that takes place when the stack becomes full depends on the state of the STVREN (Stack Over-flow Reset Enable) configuration bit. Refer to Section 20.0 for a description of the device configuration bits when Read Microcontroller.

If STVREN is set (default), the 31st push will push the (PC + 2) value onto the stack, set the STKFUL bit, and reset the device. The STKFUL bit will remain set and the stack pointer will be set to ‘0’.

If STVREN is cleared, the STKFUL bit will be set on the 31st push and the stack pointer will increment to 31. Any additional pushes will not overwrite the 31st push, and STKPTR will remain at 31 if unlock Microcontroller chip.

Since the Top-of-Stack (TOS) is readable and writable, the ability to push values onto the stack and pull values off the stack without disturbing normal program execution is a desirable option. To push the current PC value onto the stack, a PUSH instruction can be executed.

This will increment the stack pointer and load the current PC value onto the stack. TOSU, TOSH and TOSL can then be modified to place a return address on the stack.

The ability to pull the TOS value off of the stack and replace it with the value that was previously pushed onto the stack, without disturbing normal execution, is achieved by using the POP instruction. ThePOP instruction discards the current TOS by decrementing the stack pointer.

The previous value pushed onto the stack then becomes the TOS value. These resets are enabled by programming the STVREN configuration bit. When the STVREN bit is disabled, a full or underflow condition will set the appropriate STKFUL or STKUNF bit, but not cause a device RESET.

When the STVREN bit is enabled, a full or underflow will set the appropriate STKFUL or STKUNF bit and then cause a device RESET. The STKFUL or STKUNF bits are only cleared by the user software or a POR Reset.