Each port is controlled by three registers, which are also defined variables in the arduino language. The DDR register, determines whether the pin is an INPUT or OUTPUT. The PORT register controls whether the pin is HIGH or LOW, and the PIN register reads the state of INPUT pins set to input with pinMode(). The maps of the ATmega8 and ATmega168 chips show the ports. The newer Atmega328p chip follows the pinout of the Atmega168 exactly.

Referring to the pin map above, the PortD registers control Arduino digital pins 0 to 7.

[@DDRD = B11111110; // sets Arduino pins 1 to 7 as outputs, pin 0 as input DDRD = DDRD | B11111100; // this is safer as it sets pins 2 to 7 as outputs

See

• Pin Mapping of Atmega 168/328

• Sometimes you might need to set multiple output pins at exactly the same time. Calling digitalWrite(10,HIGH); followed by digitalWrite(11,HIGH); will cause pin 10 to go HIGH several microseconds before pin 11, which may confuse certain time-sensitive external digital circuits you have hooked up. Alternatively, you could set both pins high at exactly the same moment in time using PORTB |= B1100;

PINB is the input register variable It will read all of the digital input pins at the same time.

• You may need to be able to turn pins on and off very quickly, meaning within fractions of a microsecond. If you look at the source code in lib/targets/arduino/wiring.c, you will see that digitalRead() and digitalWrite() are each about a dozen or so lines of code, which get compiled into quite a few machine instructions. Each machine instruction requires one clock cycle at 16MHz, which can add up in time-sensitive applications. Direct port access can do the same job in a lot fewer clock cycles.

DDRD - The Port D Data Direction Register - read/write

PORTD - The Port D Data Register - read/write

PIND - The Port D Input Pins Register - read only

DDRB - The Port B Data Direction Register - read/write

PORTB - The Port B Data Register - read/write

PINB - The Port B Input Pins Register - read only

DDRC - The Port C Data Direction Register - read/write

PORTC - The Port C Data Register - read/write

PINC - The Port C Input Pins Register - read only

Referring to the pin map above, the PortD registers control Arduino digital pins 0 � 7.

[@DDRD = B11111110; // sets Arduino pins 1 � 7 as outputs, pin 0 as input DDRD = DDRD | B11111100; // this is safer � it sets pins 2 to 7 as outputs

PINB is the input register variable � it will read all of the digital input pins at the same time.

• It is a lot easier to cause unintentional malfunctions with direct port access. Notice how the line DDRD = B11111110; above mentions that it must leave pin 0 as an input pin. Pin 0 is the receive line (RX) on the serial port. It would be very easy to accidentally cause your serial port to stop working by changing pin 0 into an output pin! Now that would be very confusing when you suddenly are unable to receive serial data, wouldn't it?

• It is a lot easier to cause unintentional malfunctions with direct port access. Notice how the line DDRD = B11111110; above mentions that it must leave pin 0 as an input pin. Pin 0 is the receive line (RX) on the serial port. It would be very easy to accidentally cause your serial port to stop working by changing pin 1 into an output pin! Now that would be very confusing when you suddenly are unable to receive serial data, wouldn't it?

Each port is controlled by three registers, which are also defined variables in the arduino language. The DDR register, determines whether the pin is an INPUT or OUTPUT. The PORT register controls whether the pin is HIGH or LOW, and the PIN register reads the state of INPUT pins set to input with pinMode(). The maps of the ATmega8 and ATmega168 chips show the ports.

Each port is controlled by three registers, which are also defined variables in the arduino language. The DDR register, determines whether the pin is an INPUT or OUTPUT. The PORT register controls whether the pin is HIGH or LOW, and the PIN register reads the state of INPUT pins set to input with pinMode(). The maps of the ATmega8? and ATmega168 chips show the ports.

Each port is controlled by three registers, which are also defined variables in the arduino language. The DDR register, determines whether the pin is an INPUT or OUTPUT. The PORT register controls whether the pin is HIGH or LOW, and the PIN register reads the state of INPUT pins set to input with pinMode(). The maps of the ATmega8? and ATmega168 chips show the ports.

Each port is controlled by three registers, which are also defined variables in the arduino language. The DDR register, determines whether the pin is an INPUT or OUTPUT. The PORT register controls whether the pin is HIGH or LOW, and the PIN register reads the state of INPUT pins set to input with pinMode(). The maps of the ATmega8? and ATmega168 chips show the ports.

Each port is controlled by three registers, which are also defined variables in the arduino language. The DDR register, determines whether the pin is an INPUT or OUTPUT. The PORT register controls whether the pin is HIGH or LOW, and the PIN register reads the state of INPUT pins set to input with pinMode(). The maps of the ATmega8and?ATmega168 chips show the ports.

Each port is controlled by three registers, which are also defined variables in the arduino language. The DDR register, determines whether the pin is an INPUT or OUTPUT. The PORT register controls whether the pin is HIGH or LOW, and the PIN register reads the state of INPUT pins.

Each port is controlled by three registers, which are defined variables in the arduino language. The DDR register, determines whether the pin is an INPUT or OUTPUT. The PORT register controls whether the pin is HIGH or LOW, and the PIN register reads the state of INPUT pins.

DDR and PORT registers may be both written to, and read. PIN registers correspond to the state of inputs and may only be read.

PIND – The Port D Input Pins Register - read only

PORTC maps to Arduino analog pins 0 to 5. Pins 6 & 7 are only accessible on the Arduino Mini

Each port is controlled by three registers, which are defined variables in the arduino language. The DDR registers, and PORT registers may be both written to, and read. PIN registers correspond to the state of inputs and may only be read.

PIND – The Port D Input Pins Register - this is read only

PINB – The Port B Input Pins Register - read only

PINC – The Port C Input Pins Register

PORTC maps to Arduino analog pins 0 to 5. Pins 6 & 7 are only accessible on the Arduino Mini\\

PORTC maps to Arduino analog pins 0 to 5.\\

DDRD – The Port D Data Direction Register

PORTD – The Port D Data Register

PIND – The Port D Input Pins Address

PORTB maps to Arduino digital pins 8 to 13 The two high bits (6 & 7) map to the crystal pins and are not usable

DDRB – The Port B Data Direction Register

PORTB – The Port B Data Register

PINB – The Port B Input Pins Address

PORTC maps to Arduino analog pins 0 to 5 pins 6 & 7 are only accessible on the Arduino Mini
-->DDRC – The Port C Data Direction Register

PORTC – The Port C Data Register

PINC – The Port C Input Pins Address

PORTD – The Port D Data Register

PIND – The Port D Input Pins Address

DDRD – The Port D Data Direction Register

   PORTD – The Port D Data Register
   PIND – The Port D Input Pins Address

PORTD maps to Arduino digital pins 0 to 7

    DDRD – The Port D Data Direction Register
    PORTD – The Port D Data Register
    PIND – The Port D Input Pins Address

:DDRD – The Port D Data Direction Register :PORTD – The Port D Data Register :PIND – The Port D Input Pins Address

  PORTD – The Port D Data Register
  PIND – The Port D Input Pins Address

Each port is controlled by three registers, which are defined variables in the arduino language

PORTD maps to Arduino digital pins 0 to 7

Each port is controlled by three registers (substitute the

PORTD maps to Arduino digital pins 0 to 7

DDRD – The Port D Data Direction Register PORTD – The Port D Data Register PIND – The Port D Input Pins Address

PORTB maps to Arduino digital pins 8 to 13 The two high bits (6 & 7) map to the crystal pins and are not usable

DDRB – The Port B Data Direction Register PORTB – The Port B Data Register PINB – The Port B Input Pins Address

PORTC maps to Arduino analog pins 0 to 5 pins 6 & 7 are only accessible on the Arduino Mini

DDRC – The Port C Data Direction Register PORTC – The Port C Data Register PINC – The Port C Input Pins Address

Examples

Why use port manipulation?

Each bit of these registers corresponds to a single pin; e.g. the low bit of DDRB, PORTB, and PINB refers to pin PB0 (digital pin 8). For a complete mapping of Arduino pin numbers to ports and bits, see the diagram for your chip: ATmega8, ATmega168. (Note that some bits of a port may be used for things other than i/o; be careful not to change the values of the register bits corresponding to them.)

Port registers allow for lower-level and faster manipulation of the i/o pins of the microcontroller on an Arduino board. The chips used on the Arduino board (the ATmega8 and ATmega168) have three ports:

• B (digital pin 8 to 13)
• C (analog input pins)
• D (digital pins 0 to 7)

Each port is controlled by three registers (substitute the letter of the port for the "x"):

• DDRx sets the direction of each pin (input or output):
• PORTx sets the output of the pin (high or low)
• PINx reads the input on each pin

Each bit of these registers corresponds to a single pin; e.g. the low bit of DDRB, PORTB, and PINB refers to pin PB0 (digital pin 8). For a complete mapping of Arduino pin numbers to ports and bits, see the diagram for your chip: ATmega8, ATmega168.

Port registers allow for lower-level and faster manipulation of the i/o pins of the microcontroller on an Arduino board. The chips used on the Arduino board (the ATmega8 and ATmega168) have three ports: B (digital pin 8 to 13), C (analog input pins), and D (digital pins 0 to 7). Each port is controlled by three registers: DDRx sets the direction of each pin (input or output), PORTx sets the output of the pin (high or low), and PINx reads the input on each pin (substitute the letter of the port for the "x"). Each bit of these registers corresponds to a single pin; e.g. the low bit of DDRB, PORTB, and PINB refers to pin PB0 (digital pin 8). For a complete mapping of Arduino pin numbers to ports and bits, see the diagram for your chip: ATmega8, ATmega168.

Port registers allow for lower-level and faster manipulation of the i/o pins of the microcontroller on an Arduino board. The chips used on the Arduino board (the ATmega8 and ATmega168) have three ports: B (digital pin 8 to 13), C (analog input pins), and D (digital pins 0 to 7). Each port is controlled by three registers: DDRx sets the direction of each pin (input or output), PORTx sets the output of the pin (high or low), and PINx reads the input on each pin (substitute the letter of the port for the "x").

Port Registers

Port registers allow for lower-level and faster manipulation of the i/o pins of the microcontroller on an Arduino board. Each port contains up to 8 pins and is controlled by three registers: one to set the direction of each pin (input or output), one to set the output of the pin (high or low), and one to read the input on the pin (high or low).

	                  // without changing the value of pins 0 & 1, which are RX & TX @]

DDRD is the direction register for Port D (Arduino digital pins 0-7). The bits in this register control whether the pins in PORTD are configured as inputs or outputs so, for example:

The Bitmath Tutorial in the Playground

From The Bitmath Tutorial

From The Bitmath Tutorial in the Playground

DDRB is the direction register for Port D. The bits in this register control whether the pins in PORTD are configured as inputs or outputs so, for example:

PINB is the input register variable – it will read all of the digital input pins at the same time.

//See the bitwise operators reference pages and

PORTD = B10101000; // sets digital pins 7,5,3 HIGH

Generally speaking, doing this sort of thing is not a good idea. Why not? Here are a few reasons:

• The code is much more difficult for you to debug and maintain, and is a lot harder for other people to understand. It only takes a few microseconds for the processor to execute code, but it might take hours for you to figure out why it isn't working right and fix it! Your time is valuable, right? But the computer's time is very cheap, measured in the cost of the electricity you feed it. Usually it is much better to write code the most obvious way.

• The code is less portable. If you use digitalRead() and digitalWrite(), it is much easier to write code that will run on all of the Atmel microcontrollers, whereas the control and port registers can be different on each kind of microcontroller.

• It is a lot easier to cause unintentional malfunctions with direct port access. Notice how the line DDRD = B11111101; above mentions that it must leave pin 1 as an input pin. Pin 1 is the receive line on the serial port. It would be very easy to accidentally cause your serial port to stop working by changing pin 1 into an output pin! Now that would be very confusing when you suddenly are unable to receive serial data, wouldn't it?

• If you are running low on program memory, you can use these tricks to make your code smaller. It requires a lot fewer bytes of compiled code to simultaneously write a bunch of hardware pins simultaneously via the port registers than it would using a for loop to set each pin separately. In some cases, this might make the difference between your program fitting in flash memory or not!

	                  // without changing the value of pins 0 & 1 @]

• It is a lot easier to cause unintentional malfunctions with direct port access. Notice how the line DDRD = B11111101; above mentions that it must leave pin 1 as an input pin. Pin 1 is the receive line on the serial port. It would be very easy to accidentally cause your serial port to stop working by changing pin 1 into an output pin! Now that would be very confusing when you suddenly are unable to receive serial data, wouldn't it?

• If you are running low on program memory, you can use these tricks to make your code smaller. It requires a lot fewer bytes of compiled code to simultaneously write a bunch of hardware pins simultaneously via the port registers than it would using a for loop to set each pin separately. In some cases, this might make the difference between your program fitting in flash memory or not!

• Sometimes you might need to set multiple output pins at exactly the same time. Calling digitalWrite(10,HIGH); followed by digitalWrite(11,HIGH); will cause pin 10 to go HIGH several microseconds before pin 11, which may confuse certain time-sensitive external digital circuits you have hooked up. Alternatively, you could set both pins high at exactly the same moment in time using PORTB |= B1100;

• You may need to be able to turn pins on and off very quickly, meaning within fractions of a microsecond. If you look at the source code in lib/targets/arduino/wiring.c, you will see that digitalRead() and digitalWrite() are each about a dozen or so lines of code, which get compiled into quite a few machine instructions. Each machine instruction requires one clock cycle at 16MHz, which can add up in time-sensitive applications. Direct port access can do the same job in a lot fewer clock cycles.

Why use port manipulation?

From The Bitmath Tutorial

Generally speaking, doing this sort of thing is not a good idea. Why not? Here are a few reasons:

    * The code is much more difficult for you to debug and maintain, and is a lot harder for other people to understand. It only takes a few microseconds for the processor to execute code, but it might take hours for you to figure out why it isn't working right and fix it! Your time is valuable, right? But the computer's time is very cheap, measured in the cost of the electricity you feed it. Usually it is much better to write code the most obvious way.

    * The code is less portable. If you use digitalRead() and digitalWrite(), it is much easier to write code that will run on all of the Atmel microcontrollers, whereas the control and port registers can be different on each kind of microcontroller.

    * It is a lot easier to cause unintentional malfunctions with direct port access. Notice how the line DDRD = B11111101; above mentions that it must leave pin 1 as an input pin. Pin 1 is the receive line on the serial port. It would be very easy to accidentally cause your serial port to stop working by changing pin 1 into an output pin! Now that would be very confusing when you suddenly are unable to receive serial data, wouldn't it? 

So you might be saying to yourself, great, why would I ever want to use this stuff then? Here are some of the positive aspects of direct port access:

    * If you are running low on program memory, you can use these tricks to make your code smaller. It requires a lot fewer bytes of compiled code to simultaneously write a bunch of hardware pins simultaneously via the port registers than it would using a for loop to set each pin separately. In some cases, this might make the difference between your program fitting in flash memory or not!

    * Sometimes you might need to set multiple output pins at exactly the same time. Calling digitalWrite(10,HIGH); followed by digitalWrite(11,HIGH); will cause pin 10 to go HIGH several microseconds before pin 11, which may confuse certain time-sensitive external digital circuits you have hooked up. Alternatively, you could set both pins high at exactly the same moment in time using PORTB |= B1100;

    * You may need to be able to turn pins on and off very quickly, meaning within fractions of a microsecond. If you look at the source code in lib/targets/arduino/wiring.c, you will see that digitalRead() and digitalWrite() are each about a dozen or so lines of code, which get compiled into quite a few machine instructions. Each machine instruction requires one clock cycle at 16MHz, which can add up in time-sensitive applications. Direct port access can do the same job in a lot fewer clock cycles. 

Referring to the pin map above, the PortD registers control Arduino digital pins 0 – 7.

DDRD = B11111110;  // sets Arduino pins 1 – 7 as outputs, pin 0 as input
DDRD = DDRD | B11111100;  // this is safer – it sets pins 2 to 7 as outputs
	                  // without changing the value of pins 0 & 1

See the bitwise operators reference pages and The Bitmath Tutorial

PORTD = B10101000; // sets digital pins 7,5,3 HIGH.

You will only see 5 volts on these pins however if the pins have been set as outputs using the DDRD register or with pinMode().

PORTD maps to Arduino digital pins 0 to 7

PORTB maps to Arduino digital pins 8 to 13 The two high bits (6 & 7) map to the crystal pins and are not usable

PORTC maps to Arduino analog pins 0 to 5 pins 6 & 7 are only accessible on the Arduino Mini

PORTD maps to Arduino digital pins 0 to 7

PORTD maps to Arduino digital pins 0 to 7

PORTD maps to Arduino digital pins 0 to 7

DDRB – The Port B Data Direction Register
PORTB – The Port B Data Register
PINB – The Port B Input Pins Address

DDRD – The Port D Data Direction Register
PORTD – The Port D Data Register\\

DDRC – The Port C Data Direction Register
PORTC – The Port C Data Register\\

		          // see the bitwise operators reference

	                  // without changing the value of pins 0 & 1
		          // the the bitwise operators reference

Atmega Port Manipulation

Atmega168 Register Descriptions

DDRB – The Port B Data Direction Register PORTB – The Port B Data Register PINB – The Port B Input Pins Address

DDRD – The Port D Data Direction Register PORTD – The Port D Data Register PIND – The Port D Input Pins Address

DDRC – The Port C Data Direction Register PORTC – The Port C Data Register PINC – The Port C Input Pins Address

Register use details

Referring to the pin map above, the PortB registers control Arduino digital pins 0 – 7.

You should note, however, that pins 0 & 1 are used for serial communications for programming and debugging the Arduino, so changing these pins should usually be avoided unless needed for serial input or output functions. Be aware that this can interfere with program download or debugging.

DDRB is the direction register for Port B. The bits in this register control whether the pins in PORTB are configured as inputs or outputs so, for example:

DDRB = B11111110;  // sets Arduino pins 1 – 7 as outputs, pin 0 as input
DDRB = DDRB | B11111100;  // this is safer – it sets pins 2 to 7 as outputs
				     // without changing the value of pins 0 & 1
				// the the bitwise operators reference

PORTB is the register for the state of the outputs. For example;

PORTB = B10101000; // sets digital pins 7,5,3 HIGH.

You will only see 5 volts on these pins however if the pins have been set as outputs using the DDRB register or with pinMode().

PINB is the input register variable – it will read all of the digital pins at one time.

Why use port manipulation? Arduino functions such as digitalWrite also ultimately end up manipulating these Port Variables, because they are really the only way to control the state of the pins on the Atemga chip.