Reverse Engineering Microcontroller ATmega169A and copy mcu atmega169a Binary from its flash and eeprom memory, the tamper resistance system of microcontroller atmega169a will be unlocked;
When changing the TOP value the program must ensure that the new TOP value is higher or equal to the value of all of the Compare Registers.
If the TOP value is lower than any of the Compare Registers, a compare match will never occur between the TCNTn and the OCRnx. Note that when using fixed TOP values, the unused bits are masked to zero when any of the OCRnx Registers are written if attack pic18f66k90 MICROCONTROLLER memory.
As the third period shown in Figure 56 illustrates, changing the TOP actively while the Timer/Counter is running in the phase correct mode can result in an unsymmetrical output. The reason for this can be found in the time of update of the OCRnx Register.
Since the OCRnx update occurs at TOP, the PWM period starts and ends at TOP. This implies that the length of the falling slope is determined by the previous TOP value, while the length of the rising slope is determined by the new TOP value.
When these two values differ the two slopes of the period will differ in length. The difference in length gives the unsymmetrical result on the output.
crack ATmega169a microcomputer fuse bit and readout firmware program from flash of ATmega169a microcontroller
It is recommended to use the phase and frequency correct mode instead of the phase correct mode when changing the TOP value while the Timer/Counter is running. When using a static TOP value there are practically no differences between the two modes of operation when recover mc9s08dz32 MICROCONTROLLER embedded firmware.
In phase correct PWM mode, the compare units allow generation of PWM waveforms on the OCnx pins. Setting the COMnx1:0 bits to two will produce a non-inverted PWM and an inverted PWM output can be generated by setting the COMnx1:0 to three.
The actual OCnx value will only be visible on the port pin if the data direction for the port pin is set as output (DDR_OCnx). The PWM waveform is generated by setting (or clearing) the OCnx Register at the compare match between OCRnx and TCNTn when the counter increments, and clearing (or setting) the OCnx Register at compare match between OCRnx and TCNTn when the counter decrements.
The PWM frequency for the output when using phase correct PWM can be calculated by the following equation:
The N variable represents the prescaler divider (1, 8, 64, 256, or 1024). The extreme values for the OCRnx Register represent special cases when generating a PWM waveform output in the phase correct PWM mode.
unlock atmega169a microprocessor fuse bit and extract source code from flash memory of atmega169a mcu
If the OCRnx is set equal to BOTTOM the output will be continuously low and if set equal to TOP the output will be continuously high for non-inverted PWM mode.
For inverted PWM the output will have the opposite logic values. If OCR1A is used to define the TOP value (WGM13:0 = 11) and COM1A1:0 = 1, the OC1A output will toggle with a 50% duty cycle.