* a resistor in series connected to ground. * The anode of an LED is connected to pin 7 with * values of pins 0 and 1 in the DDRD and PORTD registers. * Demonstration using bank D pins 0 - 7 and preserving the In order to preserve a bit you can OR it against 0 or AND it against 1.įollow along with the documentation in the program to see how this works.īuild the circuit shown in the diagram, you will need:Ĭopy this program into the Arduino IDE and upload it to your Arduino: /********************************************************* Here is a truth table for a logical AND: 0 & 0 = 0 The ampersand (&) is the symbol for a logical AND. Here is a truth table for a logical OR: 0 | 0 = 0Ī logical AND compares two bytes bit for bit and the result is 1 only if both bits are 1. The vertical line (|) is the symbol for a logical OR. Bit 0 is 2^0, bit 1 is 2^1, etc.Ī logical OR compares two bytes bit for bit and the result is 1 if either or the bytes is 1, if not the result is 0. This requires the use of logical AND and OR commands.Įach register is 8 bits numbered 0 to 7 from right to left. So for safety it is best to preserve the values of bits 0 and 1 in the DDRD and PORTD registers. Things can get weird if you mess with these pins. Most Arduino enthusiasts do not try to use these pins for anything else. It will even work if the values are in variables, binary or decimal: int on = B00100000 Īs mentioned in step 1 bits six and seven are mapped to the crystal, just leave them alone and you will be all right.īank D controls pins 0 - 7, but pins 0 and 1 are used for serial communication. Here is an example with decimal numbers: void setup() ![]() It will also work with decimal numbers, use whatever is most convenient. The bits are numbered 0 to 7, the right most bit is the zero bit (2^0). The "B" before the number tells the compiler to interpret the number as binary. * by changing the PORTB register instead of using digitalWrite(). ![]() * Turn the LED attached to B5 (Digital pin 13) on and off * Set B5 (Digital pin 13) to output by changing the DDRB Copy these programs into the Arduino IDE and upload them to your Arduino. ( If you would like to have unrestricted use of all eight pins on a register try working with the Attiny84 chip.)įor these first programs all that is needed is a working Arduino, we will be blinking the internal LED on digital pin 13. I will explain the restrictions in the following steps. Sadly the Arduino does not have a bank that gives you unrestricted use of eight pins. D1 = digital pin 1, used for serial communication, save it's state.D0 = digital pin 0, used for serial communication, save it's state.C7 = analog pin 7, available only on Arduino mini.C6 = analog pin 6, available only on Arduino mini. ![]() B7 is mapped to the crystal, do not use.B6 is mapped to the crystal, do not use.Here is a list of the pins and the corresponding registers: If the DDR register is set to input 1 turns on the internal pull-up resistor.Įach pin is one bit on the controlling registers.If the DDR register is set to output 0 sets the pin low and 1 sets it high.The PIN register is used to read the digital value of the pin.The DDR register is the data direction, 0 = input, 1 = output.There are three banks of pins on the Atmega 328 and 168 microcontrollers called B, C, and D.Įach bank of pins has three 8 bit registers used to control it: It is possible to use lower level commands to greatly speed up the input/output. In order to keep it simple I switched to four LEDS to solve the problem. It worked fine the first time through but the longer it ran more mixed up the timing became. When writing this instructable I found out how much. If you have a time critical program digitalRead() and digitalWrite() can slow it down a lot. next we want to set up the RPM reading.On the Arduino, and all Atmel microcontrollers, processing is fast when using the Arduino IDE. Set up the pins - first we want to set the duty-cycle to be at 25,000 Hz for PWM Control Reading this forum and some other links I found I have put together the following code: // Declare variablesįloat elapsedMS = (millis() - lastRPMmillis)/1000.0 įloat revPerMS = revolutions / elapsedMS I'm a complete Arduino Newbie trying to do a project controlling a 120mm 4 pin case fan using an Arduino MEGA 2560.
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