Extract MCU AT89C51AC3 Code out from flash and eeprom memory after unlock microcontroller, the status of MCU will be reset from encrypted to decrypted by cut off the security fuse bit;
Software can take advantage of the additional data pointers to both increase speed and reduce code size, for example, block operations (copy, compare…) are well served by using one data pointer as a “source” pointer and the other one as a “destination” pointer.
Hereafter is an example of block move implementation using the two pointers and coded in assembler. The latest C compiler takes also advantage of this feature by providing enhanced algorithm libraries. The INC instruction is a short (2 Bytes) and fast (6 machine cycle) way to manipulate the DPS bit in the AUXR1 register. However, note that the INC instruction does not directly force the DPS bit to a particular state, but simply toggles it. In simple routines, such as the block move example, only the fact that DPS is toggled in the proper sequence matters, not its actual value. In other words, the block move routine works the same whether DPS is ‘0’ or ‘1’ on entry.
Note:
If VCC was reduced during the Power-Down mode, do not exit Power-Down mode until VCC is restored to the normal operating level. There are two ways to exit the Power-Down mode:
- Generate an enabled external interrupt.
Note:
The AT89C51AC3 provides capability to exit from Power-Down using INT0#, INT1#. Hardware clears PD bit in PCON register which starts the oscillator and restores the clocks to the CPU and peripherals. Using INTx# input, execution resumes when the input is released (see Figure 19). Execution resumes with the interrupt service routine. Upon completion of the interrupt service routine, program execution resumes with the instruction immediately following the instruction that activated Power-Down mode before Extract microcontroller embedded firmware.
The external interrupt used to exit Power-Down mode must be configured as level sensitive (INT0# and INT1#) and must be assigned the highest priority. In addition, the duration of the interrupt must be long enough to allow the oscillator to stabilize. The execution will only resume when the interrupt is deasserted. Exit from power-down by external interrupt does not affect the SFRs nor the internal RAM content.
The 2-Kbyte on-chip EEPROM memory block is located at addresses 0000h to 07FFh of the XRAM/ERAM memory space and is selected by setting control bits in the EECON register. A read in the EEPROM memory is done with a MOVX instruction. A physical write in the EEPROM memory is done in two steps: write data in the column latches and transfer of all data latches into an EEPROM memory row (programming).
The number of data written on the page may vary from 1 up to 128 Bytes (the page size). When programming, only the data written in the column latch is programmed and a ninth bit is used to obtain this feature. This provides the capability to program the whole memory by Bytes, by page or by a number of Bytes in a page. Indeed, each ninth bit is set when the writing the corresponding byte in a row and all these ninth bits are reset after the writing of the complete EEPROM row.
The EEPROM programming consists of the following actions:
writing one or more Bytes of one page in the column latches. Normally, all Bytes must belong to the same page; if not, the first page address will be latched and the others discarded.
launching programming by writing the control sequence (50h followed by A0h) to the EECON register. EEBUSY flag in EECON is then set by hardware to indicate that programming is in progress and that the EEPROM segment is not available for reading. The end of programming is indicated by a hardware clear of the EEBUSY flag.
