- Block Diagram of the AVR MCU Architecture. - Figure 6-2 shows the structure of the 32 general purpose working registers in the CPU.. - The Stack Pointer Register always points to the top of the Stack. - RESET has the highest priority, and next is INT0 – the External Interrupt Request 0. - The Interrupt Vectors can be moved to the start of the Boot Flash section by setting the IVSEL bit in the General Interrupt Control Register (GICR). - Refer to the description of the EEPROM Control Register for details on this.. - The I/O space definition of the ATmega32A is shown in “Register Summary” on page 334.. - The Flash clock controls operation of the Flash interface. - This option should not be used when operating close to the maximum frequency of the device.. - If Timer/Counter2 is clocked asynchronously, i.e., the AS2 bit in ASSR is set, Timer/Counter2 will run during sleep. - Refer to the description of the Watchdog Timer Control Register for details.. - Refer to the description of the WDE bit for a Watchdog disable procedure.. - When the IVSEL bit in GICR is set, interrupt vectors will be moved to the start of the Boot Flash section. - When the IVSEL bit is cleared (zero), the Interrupt Vectors are placed at the start of the Flash memory. - When this bit is set (one), the interrupt vectors are moved to the beginning of the Boot Loader section of the Flash. - The IVCE bit must be written to logic one to enable change of the IVSEL bit. - Table 12-2 summarizes the function of the overriding signals. - This might corrupt the result of the conversion.. - In the figure, the signal is connected to the output of the schmitt trigger but before the synchronizer. - When the SPI is enabled as a Slave, this pin is configured as an input regardless of the setting of DDB7. - When the SPI is enabled as a Master, this pin is configured as an input regardless of the setting of DDB6. - When the SPI is enabled as a Slave, this pin is configured as an input regardless of the setting of DDB5. - When the SPI is enabled as a Slave, this pin is configured as an input regardless of the setting of DDB4. - When the USART Transmitter is enabled, this pin is configured as an output regardless of the value of DDD1.. - When the USART Receiver is enabled this pin is configured as an input regardless of the value of DDD0. - A simpli- fied block diagram of the 8-bit Timer/Counter is shown in Figure 14-1. - The result of the compare can be used by the waveform generator to generate a PWM or variable frequency output on the Output Compare Pin (OC0). - The main part of the 8-bit Timer/Counter is the programmable bi-directional counter unit. - Figure 14-2 shows a block diagram of the counter and its surroundings.. - The counting sequence is determined by the setting of the WGM01 and WGM00 bits located in the Timer/Counter Control Register (TCCR0). - Figure 14-3 shows a block diagram of the output compare unit.. - The port override function is independent of the Waveform Generation mode.. - The mode of operation, i.e., the behavior of the Timer/Counter and the Output Compare pins, is defined by the combination of the Waveform Generation mode (WGM01:0) and Compare Output mode (COM0[1:0]) bits. - This mode allows greater control of the compare match output frequency. - This feature allows software control of the counting.. - The latch is transparent in the high period of the internal system clock.. - A simplified block diagram of the 16-bit Timer/Counter is shown in Figure 16-1. - The result of the compare can be used by the Waveform Generator to. - “Analog Comparator” on page 205.) The Input Capture unit includes a digital filtering unit (Noise Canceler) for reducing the chance of capturing noise spikes.. - The assign- ment is dependent of the mode of operation.. - Note that when using “C”, the compiler handles the 16-bit access.. - Reading any of the OCR1A/B or ICR1 Registers can be done by using the same principle.. - Writing any of the OCR1A/B or ICR1 Registers can be done by using the same principle.. - Figure 16-2 shows a block diagram of the counter and its surroundings.. - The counting sequence is determined by the setting of the Waveform Generation Mode bits (WGM13:0) located in the Timer/Counter Control Registers A and B (TCCR1A and TCCR1B).. - Alternatively the time-stamps can be used for creating a log of the events.. - When a capture is triggered, the 16-bit value of the counter (TCNT1) is written to the Input Capture Register (ICR1). - In this case the result of the capture will be incorrect.. - After a change of the edge, the Input Capture Flag (ICF1) must be cleared by software (writing a logical one to the I/O bit location). - Figure 16-4 shows a block diagram of the output compare unit. - The double buffering synchronizes the update of the OCR1x Compare. - The content of the OCR1x (Buffer or Compare) Register is only changed by a write operation (the Timer/Counter does not update this register automatically as the TCNT1 and ICR1 Register). - The general I/O port function is overridden by the Output Compare (OC1x) from the Waveform Generator if either of the COM1x1:0 bits are set. - The mode of operation, i.e., the behavior of the Timer/Counter and the output compare pins, is defined by the combination of the Waveform Generation mode (WGM13:0) and Compare Output mode (COM1x1:0) bits. - This feature is similar to the OC1A toggle in CTC mode, except the double buffer feature of the output compare unit is enabled in the fast PWM mode.. - The reason for this can be found in the time of update of the OCR1x Reg- ister. - A simpli- fied block diagram of the 8-bit Timer/Counter is shown in Figure 17-1. - The result of the compare can be used by the waveform generator to generate a PWM or variable frequency output on the Output Compare Pin (OC2). - Figure 17-2 shows a block diagram of the counter and its surrounding environment.. - The counting sequence is determined by the setting of the WGM21 and WGM20 bits located in the Timer/Counter Control Register (TCCR2). - Figure 17-3 shows a block diagram of the output compare unit.. - The mode of operation, i.e., the behavior of the Timer/Counter and the output compare pins, is defined by the combination of the Waveform Generation mode (WGM2[1:0]) and Compare Out- put mode (COM2[1:0]) bits. - 17.9 Asynchronous Operation of the Timer/Counter. - During asynchronous operation, the synchronization of the Interrupt Flags for the. - When the SPI is configured as a Master (MSTR in SPCR is set), the user can determine the direction of the SS pin.. - Typically, the pin will be driving the SS pin of the SPI Slave.. - When the DORD bit is written to one, the LSB of the data word is transmitted first.. - When the DORD bit is written to zero, the MSB of the data word is transmitted first.. - The settings of the Clock Phase bit (CPHA) determine if data is sampled on the leading (first) or trailing (last) edge of SCK. - A simplified block diagram of the USART transmitter is shown in Figure 19-1. - Figure 19-2 shows a block diagram of the clock generation logic.. - 19.3.1 Internal Clock Generation – The Baud Rate Generator. - UBRR Contents of the UBRRH and UBRRL Registers . - Note that f osc depends on the stability of the system clock source. - 19.6 Data Transmission – The USART Transmitter. - They can be optimized if the con- tents of the UCSRB is static. - 19.7 Data Reception – The USART Receiver. - bits of the data read from the UDR will be masked to zero. - None of the Error Flags can generate interrupts.. - In contrast to the Transmitter, disabling of the Receiver will be immediate. - When disabled (i.e., the RXEN is set to zero) the Receiver will no longer override the normal function of the RxD port pin. - The receiver buffer FIFO will be flushed when the Receiver is disabled, i.e., the buffer will be emptied of its contents. - Figure 19-6 shows the sampling of the data bits and the par- ity bit. - i.e., when the first stop bit of the next character in the receive buffer is zero. - The level of the data line must be stable when the clock line is high. - The MSB of the address byte is transmitted first. - The MSB of the data byte is transmitted first.. - Note that the wired-ANDing of the SCL line can be used to implement handshaking between the master and the slave. - The fact that multiple masters have started transmission at the same time should not be detectable to the slaves, i.e., the data being transferred on the bus must not be corrupted.. - 20.5 Overview of the TWI Module. - Overview of the TWI Module. - TWBR = Value of the TWI Bit Rate Register. - TWPS = Value of the prescaler bits in the TWI Status Register. - When in Transmitter mode, the value of the received (N)ACK bit can be determined by the value in the TWSR.. - In the following an assembly and C implementation of the example is given. - If the direction bit is “0” (write), the TWI will operate in SR mode, otherwise ST mode is entered. - $68 Reception of the own. - If the direction bit is “1” (read), the TWI will operate in ST mode, otherwise SR mode is entered. - $B0 Reception of the own. - After a REPEATED START, the master keeps ownership of the bus
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