Class _cta: 8-bit counter with two compare units

This class is used by:

• ATtiny24/44/84 : counter0
• ATtiny25/45/85 : counter0
• ATmega48A/PA/88A/PA/168A/PA/328/P : counter0
• ATmega16U4/32U4 : counter0

Relatives

• (COUNTER,prescaler): class _psa prescaler;
• (COUNTER,compare0): class _oca compare unit with waveform generator;
• (COUNTER,compare1): class _oca compare unit with waveform generator.

Interrupts

• (COUNTER,irq), (COUNTER,irq,overflow): triggered when the counter counts from "max" to 0 (after_max) in up_loop counting mode, or when it counts from 0 to 1 (after_bottom) in updown_loop counting mode.

Actions

hwa( configure, ... ): configure the counting unit

hwa( configure, counter0,
 
     //  How the counter is clocked
     //
     clock,       none                       // No clock, the counter is stopped
                | ioclk [/ 8|64|256|1024]    // IOCLK divided by 1,8,64,256,1024
                | external_rising            // External input, rising edge
                | external_falling,          // External input, falling edge
 
     //  How does this counter count
     //
     direction,   up_loop                    // Count from bottom to top and loop
                | updown_loop,               // Count up and down alternately
 
   [ bottom,      0, ]                       // Default, no other choice
 
     //  The maximum value the counter reaches
     //
   [ top,         0xFF | 0x00FF | 255 | max  // Hardware fixed value 0xFF (default)
                | compare0,]                 // Value stored in compare0
 
     //  When the overflow flag is set
     //
   [ overflow,    after_bottom               // When the counter counts from 0 to 1
                | after_top                  // When the counter counts from top to 0
                | after_max ]                // When the counter counts from max to 0
   );

Note

If a compare unit is used, its configuration must be done inside the same context as the counter so that HWA has all the necessary informations to choose the correct register settings.

If the optionnal argument overflow is not stated, an acceptable value will be selected according to the configuration of the compare units found in the HWA context. If overflow is stated, the validity of its value will be verified.

Atmel modes:

Mode	direction	top	overflow	Overflow flag	Compare update
0 Normal	up_loop	max	after_max	max -> 0	Immediate
1 PWM, Phase correct	updown_loop	max	after_bottom	0 -> 1	At top
2 CTC	up_loop	compare0	after_max	max -> 0	Immediate
3 Fast PWM	up_loop	max	after_max	max -> 0	At bottom
5 PWM, Phase correct	updown_loop	compare0	after_bottom	0 -> 1	At top
7 Fast PWM	up_loop	max	after_top	top -> 0	At bottom

Example 1 - An overflow IRQ is triggered when the counter counts from 255 to 0, the frequency of the IRQs is HW_SYSHZ/8/256:

hw( configure, counter0,
    clock,     ioclk/8,
    direction, up_loop,
    top,       max,
    overflow,  after_max );

Example 2 - Counting: 0-1-2-3-2-1-0-1..., an overflow IRQ is triggered when the counter counts from 0 to 1, the frequency of the IRQs is HW_SYSHZ/64/6.

hwa( configure, counter0,
     clock,     ioclk/64,
     direction, updown_loop,
     top,       compare0,
     overflow,  after_bottom );
hwa( write, (counter0,compare0), 3 );

hw( read, ... ): get the count

uint8_t n = hw( read, counter0 );

hw( write, ... ), hwa( write, ... ): set the count

hw( write, counter0, value );

hwa( write, counter0, value );

---

hw( clear, ... ): set the count to 0

hw( clear, counter0 );

Registers

Hardware registers:

• ccra: control register a
• ccrb: control register b
• count, reg: count register
• ocr0: output-compare A register
• ocr1: output-compare B register
• imsk: interrupt mask register
• ifr: interrupt flag register

Logical registers:

• wgm: counting and waveform generation mode
• cs: clock selection
• ie: overflow interrupt mask
• ocie0: compare A interrupt mask
• ocie1: compare B interrupt mask
• if: overflow interrupt flag
• ocif0: compare A interrupt flag
• ocif1: compare B interrupt flag
• com0: output-compare mode A
• com1: output-compare mode B
• foc0: force output-compare A
• foc1: force output-compare B