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en:multiasm:exercisesbook:arduinouno [2026/05/04 14:01] – [Table] ktokarzen:multiasm:exercisesbook:arduinouno [2026/05/04 14:55] (current) – [Function Call Standards] ktokarz
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 <note tip>Some GPIOs have extra features (as presented in figure {{ref>arduinoports}}), such as hardware-accelerated PWM, I2C, Serial or SPI. PWM is useful for simulating an analogue output, e.g., to control LED brightness, as we show in the following sections.</note> <note tip>Some GPIOs have extra features (as presented in figure {{ref>arduinoports}}), such as hardware-accelerated PWM, I2C, Serial or SPI. PWM is useful for simulating an analogue output, e.g., to control LED brightness, as we show in the following sections.</note>
  
-**IO Registers **\\+**I/O Registers **\\
 Each Port has assigned three 8-bit registers (there are 9 in total then): Each Port has assigned three 8-bit registers (there are 9 in total then):
   * DDRx (Data Direction Register): there are 3 of those registers, one per Port (B, C, D): DDRB, DDRC and DDRD. This registers configures GPIO as Input (0) or Output (1). Configuration is done "per bit", so it is equivalent to controlling each GPIO individually.   * DDRx (Data Direction Register): there are 3 of those registers, one per Port (B, C, D): DDRB, DDRC and DDRD. This registers configures GPIO as Input (0) or Output (1). Configuration is done "per bit", so it is equivalent to controlling each GPIO individually.
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 A common scenario for manual control of the GPIO pin is to first set either the GPIO is input or output (using the correct DDRx register), then either set (''SBI''), reset (''CBI''), check (''SBIS'', ''SBIC''), read the whole register (''IN'') or write the whole register (''OUT''). A common scenario for manual control of the GPIO pin is to first set either the GPIO is input or output (using the correct DDRx register), then either set (''SBI''), reset (''CBI''), check (''SBIS'', ''SBIC''), read the whole register (''IN'') or write the whole register (''OUT'').
-<note tip>''IN'' and ''OUT'' instructions operate on whole, 8-bit registers rather than on single bits. Those are general-purpose instructions that cover the entire range of IO registers (0-63), in addition to the aforementioned DDRx, PORTx, and PINx registers. Operating on multiple bits (8 bits) is faster than setting or reading them individually.</note>+<note tip>''IN'' and ''OUT'' instructions operate on whole, 8-bit registers rather than on single bits. Those are general-purpose instructions that cover the entire range of I/O registers (0-63), in addition to the aforementioned DDRx, PORTx, and PINx registers. Operating on multiple bits (8 bits) is faster than setting or reading them individually.</note>
  
  
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 </code> </code>
  
-The function is called when interrupt INT0 (on the falling edge of GPIO 2) occurs, and it simply toggles PB5 (GPIO 13, built-in LED). This is a trick in AVR that simplifies code: the classical read->swap->write is replaced by a single ''sbi'' instruction call, which, in the context of the GPIO registers, toggles the selected bit.+The function is called when interrupt INT0 (on the falling edge of GPIO 2) occurs, and it simply toggles PB5 (GPIO 13, built-in LED). This is a trick in AVR that simplifies code: the classical read->swap->write is replaced by a single ''sbi'' instruction, which, in the context of the GPIO registers, toggles the selected bit.
 <code asm> <code asm>
 ; --- Interrupt Service Routine --- ; --- Interrupt Service Routine ---
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 Where **Fcpu** is 16MHz for regular Arduino Uno (AtMega 328P). Note that this calculation yields ~9615 bps, not exactly 9600 bps. A tolerance of up to 2% is acceptable (here, it is 0.16%). Where **Fcpu** is 16MHz for regular Arduino Uno (AtMega 328P). Note that this calculation yields ~9615 bps, not exactly 9600 bps. A tolerance of up to 2% is acceptable (here, it is 0.16%).
  
-Next step is to enable UART:+Next step is to configure frame format (8 bits, no parity, 1 stop bit, shortly 8N1 - the most common case):
 <code asm> <code asm>
-ldi r16, (1 << TXEN0) +ldi r18, (1<<UCSZ01) | (1<<UCSZ00) 
-sts UCSR0B, r16+sts UCSR0C, r18
 </code> </code>
-and configure frame format (8 bits, no parity, 1 stop bit, shortly 8N1 - the most common case):+ 
 +and enable the UART:
 <code asm> <code asm>
 ldi r16, (1 << TXEN0) ldi r16, (1 << TXEN0)
 sts UCSR0B, r16 sts UCSR0B, r16
 </code> </code>
-Now it is time to send the string to the transmitter, byte by byte. Pointer to the string is loaded to Z register (ZH and ZL respectively) using ''ldi''. The string is processed character by character until it encounters 0 (the end of the string).+ 
 +Now it is time to send the string to the transmitter, byte by byte. A pointer to the string is loaded into the Z register (ZH and ZL, respectively) using ''ldi''. The string is processed character by character until it encounters 0 (the end of the string).
 <code asm> <code asm>
 main: main:
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 <table arduinotimerprescalers> <table arduinotimerprescalers>
-<caption>Prescalers and related frequentues and periods for typical 16MHz clock</caption>+<caption>Prescalers and related frequenties and periods for typical 16MHz clock</caption>
 ^ Prescaler ^ Frequency ^ Period (Tick Speed) ^ ^ Prescaler ^ Frequency ^ Period (Tick Speed) ^
 | 1 | 16 MHz | 0.0625 µs | | 1 | 16 MHz | 0.0625 µs |
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 ** The Notification **\\ ** The Notification **\\
-These registers are to control the timer-based interrupt notification system. We do not use interrupts for PWM; therefore, this description is omitted.+These registers are to control the timer-based interrupt notification system. We do not use interrupts for PWM, but they are necessary for handling timer-based tasks.
  
 <table arduinothemanagertimer> <table arduinothemanagertimer>
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 Start conversion by setting the ADSC bit (6) of ADSCRA to 1.  Start conversion by setting the ADSC bit (6) of ADSCRA to 1. 
-ADC requires some time to read the value and complete the conversion (it is based on a capacitor); thus, when it is ready to read, the ADSC bit is cleared by the ADC hardware.+ADC requires some time to complete the conversion; thus, when the result is ready to read, the ADSC bit is cleared by the ADC hardware.
 Here, we do not use any interrupts, just dummy pulling. Here, we do not use any interrupts, just dummy pulling.
 <code asm> <code asm>
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 ** Speed vs Quality ** ** Speed vs Quality **
-ADC converts an analogue value to its digital representation using a capacitor. Charging and discharging of the capacitor require time and depend on the impedance of the analogue signal's input source. The general rule says that the faster the conversion, the lower the quality and the higher the error ratio. Conversion speed can be controlled using a prescaler value (bits ADPS2, ADPS1, and ADPS0 of the ADCSRA register). The prescaler divides the clock frequency (16MHz) to slow down the conversion process. Prescaler value and related conversion speed and time is presented in table {{ref>arduinoadcprescaler}}.+ADC converts an analogue value to its digital representation using a method called successive approximation, measuring the voltage stored in a capacitor. Charging and discharging of the capacitor require time and depend on the impedance of the analogue signal's input source. The general rule says that the faster the conversion, the lower the quality and the higher the error ratio. Conversion speed can be controlled using a prescaler value (bits ADPS2, ADPS1, and ADPS0 of the ADCSRA register). The prescaler divides the clock frequency (16MHz) to slow down the conversion process. Prescaler value and related conversion speed and time are presented in table {{ref>arduinoadcprescaler}}.
  
 <table arduinoadcprescaler> <table arduinoadcprescaler>
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 To use a string (e.g. constant) that is stored in Flash, convert this line: To use a string (e.g. constant) that is stored in Flash, convert this line:
 ''ld   r18, Z+'' -> ''lpm   r18, Z+''.</note> ''ld   r18, Z+'' -> ''lpm   r18, Z+''.</note>
-<note important>If you run this function in a loop, give it a delay after each Serial port sending session is finished to let the hardware clean buffers. </note>+<note important>If you run this function in a loop, add a delay after each Serial port sending session to let the hardware clear buffers. </note>
  
 ** Delay (in ms) **\\ ** Delay (in ms) **\\
en/multiasm/exercisesbook/arduinouno.1777892487.txt.gz · Last modified: by ktokarz
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