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pins.md

Algorithm

PWM generation

PWM signal is generated by timers.

RPM measurement

RPM is measured by finding time between two RPM pulses using the 16-bit Timer1. Pulses are detected using polling on input pins.

Atmega88 pin allocation

Atmega88 pinout

  • pin 1: reset, connected to VCC and protected by zener diode
  • pin 2: USART RX line (pullup?)
  • pin 3: USART TX line
  • pin 4: PD2, Error signal output
  • pin 5: PD3, OC2B, fan 4 PWM output
  • pin 6: PD4, not connected
  • pin 7: VCC
  • pin 8: GND
  • pin 9: XTAL 1
  • pin 10: XTAL 2
  • pin 11: PD5, OC0B, fan 2 PWM output
  • pin 12: PD6, OC0A, fan 1 PWM output
  • pin 13: PD7, not connected
  • pin 14: PB0, fan 1 enable
  • pin 15: PB1, fan 2 enable
  • pin 16: PB2, fan 3 enable
  • pin 17: PB3, fan 3 PWM output
  • pin 18: PB4, fan 4 enable
  • pin 19: PB5, not connected
  • pin 20: AVCC, connected to VCC through low-pass filter L1/C13
  • pin 21: AREF, analog reference, decoupled with 100nF cap C10
  • pin 22: GND
  • pin 23: PC0, ADC0, temperature sensor 1 input, low-pass filter R5/C7
  • pin 24: PC1, ADC1, temperature sensor 2 input, low-pass filter R3/C8
  • pin 25: PC2, fan 1 RPM input, pull-up, low-pass filter R10/C9
  • pin 26: PC3, fan 2 RPM input, pull-up, low-pass filter R9/C11
  • pin 27: PC4, fan 3 RPM input, pull-up, low-pass filter R8/C12
  • pin 28: PC5, fan 4 RPM input, pull-up, low-pass filter R7/C14

Port directions

Port B

  • PB0 - output (fan 1 enable)
  • PB1 - output (fan 2 enable)
  • PB2 - output (fan 3 enable)
  • PB3 - output (fan 3 PWM)
  • PB4 - output (fan 4 enable)
  • PB5 - output (not connected)
  • PB6 - output (overriden by xtal)
  • PB7 - output (overriden by xtal)

Port C

  • PC0 - input (ADC)
  • PC1 - input (ADC)
  • PC2 - input (fan 1 RPM, pull-up)
  • PC3 - input (fan 2 RPM, pull-up)
  • PC4 - input (fan 3 RPM, pull-up)
  • PC5 - input (fan 4 RPM, pull-up)
  • PC6 - input (default reset config)
  • PC7 - not in circuit/registry

Port D

  • PD0 - output (overriden by USART)
  • PD1 - output (overriden by USART)
  • PD2 - output (error)
  • PD3 - output (fan 4 PWM)
  • PD4 - output (not connected)
  • PD5 - output (fan 2 PWM)
  • PD6 - output (fan 1 PWM)
  • PD7 - output (not connected)

Fuses

Clock selection: full swing crystal

  • CKSEL 0111
  • SUT 11 (slow raising power)
  • Low fuse result: 0xf7

Registers

  • OSCCAL - Oscillator calibration register - NO CHANGE
  • CLKPR - Clock prescale register - NO CHANGE
  • SMCR - Sleep mode control register - NO CHANGE
  • PRR - Power reduction register - NO CHANGE
  • MCUSR - MCU status register - NO CHANGE
  • WDTCSR - Watchdog timer control register - NO CHANGE
  • MCUCR - MCU control register - interrupts through sei()
  • EICRA - External interrupt control register A - NO CHANGE
  • EIMSK - External interrupt mask register - NO CHANGE
  • EIFR - External interrupt flag register - NO CHANGE
  • PCICR - Pin change interrupt control register - NO CHANGE
  • PCIFR - Pin change interrupt flag register - NO CHANGE
  • PCMSK2 - Pin change mask register 2 - NO CHANGE
  • PCMSK1 - Pin change mask register 1 - NO CHANGE
  • PCMSK0 - Pin change mask register 0 - NO CHANGE
  • PINB - The port B input pins address - NOT USED
  • PIND - The port D input pins address - NOT USED
  • GTCCR - General timer/counter control register - NO CHANGE
  • SPCR – SPI control register - NO CHANGE
  • SPSR – SPI status register - NOT USED
  • SPDR – SPI data register - NOT USED

Port B

  • DDRB - The port B data direction register. As port B is configured as output then all bit are set to 1.
  • PORTB - The port B data register. Used for controlling the fans.

Port C

  • DDRC - The port C data direction register- As port C is used as input then no change is needed as it is configured as input by default.
  • PORTC - The port C data register. Some bits need to be written 1 to enable pull-ups.
  • PINC - The port C input pins address. Used for polling fans PWM.

Port D

  • PORTD - The port D data register. Used for error signal. Other functions are overriden (USART, PWM).
  • DDRD - The port D data direction register. As port B is configured as output then all bit are set to 1.

Timer 0

Timer 0 needs to be configured in phase-correct PWM mode.

  • TCCR0A - Timer/counter control register A.
  • TCCR0B - Timer/counter control register B.
  • TCNT0 - Timer/counter register.
  • OCR0A - Output compare register A.
  • OCR0B - Output compare register B.
  • TIMSK0 - Timer/counter interrupt mask register - NO CHANGE
  • TIFR0 - Timer/Counter0 interrupt flag register - NO CHANGE

Timer 1

Timer 1 is used for counting time between RPM pulses and detecting timeout.

  • TCCR1A – Timer/Counter1 control register A.
  • TCCR1B – Timer/Counter1 control register B.
  • TCCR1C – Timer/Counter1 control register C - NO CHANGE
  • TCNT1H and TCNT1L – Timer/Counter1.
  • OCR1AH and OCR1AL – Output compare register 1 A.
  • OCR1BH and OCR1BL – Output compare register 1 B.
  • ICR1H and ICR1L – Input capture register 1. NO CHANGE/NOT USED
  • TIMSK1 – Timer/Counter1 interrupt mask register
  • TIFR1 – Timer/Counter1 interrupt flag register

Timer 2

Timer 2 needs to be configured in phase-correct PWM mode.

  • TCCR2A – Timer/counter control register A.
  • TCCR2B – Timer/counter control register B.
  • TCNT2 – Timer/counter register.
  • OCR2A – Output compare register A.
  • OCR2B – Output compare register B.
  • TIMSK2 – Timer/Counter2 interrupt mask register - NO CHANGE
  • TIFR2 – Timer/Counter2 interrupt flag register - NO CHANGE
  • ASSR – Asynchronous status register - NO CHANGE

USART

TODO

ADC

ADC reference is set to AVcc.

  • ADCSRB – ADC Control and Status Register B - NO CHANGE
  • ACSR – Analog Comparator Control and Status Register - NO CHANGE
  • DIDR1 – Digital Input Disable Register 1 - NO CHANGE
  • ADMUX – ADC Multiplexer Selection Register
  • ADCSRA – ADC Control and Status Register A
  • ADCL and ADCH – The ADC Data Register
  • ADCSRB – ADC Control and Status Register B
  • DIDR0 – Digital Input Disable Register 0

FIXME - use watchdog? ]]>http://www.embedds.com/using-watchdog-timer-in-your-projects/]]>

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