Difference between revisions of "How to install Arduino Library"

Latest revision as of 03:47, 7 November 2015

Addressing

EachPCF8591deviceinanI 2 C-bussystemisactivatedby sending a valid address to the device. The address consists of a fixed part and a programmable part. The programmable part must be set according to the address pins A0, A1 and A2. The address always has to be sent as the first byte after the start condition in the I 2 C-bus protocol. The last bit of the address byte is the read/write-bit which sets the direction of the following data transfer (see Figs 4). lianjie

• Figs 4

https://www.arduino.cc/en/Main/Software

Control byte=

The second byte sent to a PCF8591 device will be stored in its control register and is required to control the device function.Theuppernibbleofthecontrolregisterisusedfor enabling the analog output, and for programming the analog inputs as single-ended or differential inputs.The lower nibble selects one of the analog input channels defined by the upper nibble (see Fig.5).If the auto-increment flag is set, the channel number is incremented automatically after each A/D conversion.
If the auto-increment mode is desired in applications where the internal oscillator is used, the analog output enable flag in the control byte (bit 6) should be set. This allows the internal oscillator to run continuously, thereby preventing conversion errors resulting from oscillator start-up delay. The analog output enable flag may be reset at other times to reduce quiescent power consumption.
The selection of a non-existing input channel results in the highest available channel number being allocated. Therefore, if the auto-increment flag is set, the next selected channel will be always channel 0. The most significant bits of both nibbles are reserved for future functions and have to be set to logic 0. After a Power-on reset condition all bits of the control register are reset to logic 0. The D/A converter and the oscillator are disabled for power saving. The analog output is switched to a high-impedance state.

• Fig.5

D/A conversion

The third byte sent to a PCF8591 device is stored in the DAC data register and is converted to the corresponding analog voltage using the on-chip D/A converter. This D/A converter consists of a resistor divider chain connected to the external reference voltage with 256 taps and selection switches. The tap-decoder switches one of these taps to the DAC output line (see Fig.6).
The analog output voltage is buffered by an auto-zeroed unity gain amplifier. This buffer amplifier may be switched on or off by setting the analog output enable flag of thecontrol register. In the active state the output voltage is held until a further data byte is sent.
The on-chip D/A converter is also used for successive approximation A/D conversion. In order to release the DAC for an A/D conversion cycle the unity gain amplifier is equippedwithatrackandholdcircuit.Thiscircuitholdsthe output voltage while executing the A/D conversion.
The output voltage supplied to the analog output AOUT is given by the formula shown in Fig.7. The waveforms of a D/A conversion sequence are shown in Fig.8.

• Fig.6

• • Fig.7

• • • Fig.8

The A/D converter makes use of the successive approximation conversion technique. The on-chip D/A converter and a high-gain comparator are used temporarily during an A/D conversion cycle.
An A/D conversion cycle is always started after sending a valid read mode address to a PCF8591 device. The A/D conversion cycle is triggered at the trailing edge of the acknowledge clock pulse and is executed while transmitting the result of the previous conversion (see Fig.9).
Once a conversion cycle is triggered an input voltage sample of the selected channel is stored on the chip and is converted to the corresponding 8-bit binary code.Samples picked up from differential inputs are converted to an 8-bit twos complement code (see Figs 10 and 11).
The conversion result is stored in the ADC data register and awaits transmission. If the auto-increment flag is set the next channel is selected.
The first byte transmitted in a read cycle contains the conversion result code of the previous read cycle. After a Power-on reset condition the first byte read is a hexadecimal 80. The maximum A/D conversion rate is given by the actual speed of the I 2 C-bus.

1. Fig.9

1. • Fig.10

1. • Fig.11

Reference voltage

For the D/A and A/D conversion either a stable external voltage reference or the supply voltage has to be applied to the resistor divider chain (pins V REF and AGND). The AGND pin has to be connected to the system analog ground and may have a DC off-set with reference to V SS . A low frequency may be applied to the V REF and AGND pins. This allows the use of the D/A converter as a one-quadrant multiplier; see Chapter 15 and Fig.7. The A/D converter may also be used as a one or two quadrant analog divider. The analog input voltage is divided by the reference voltage. The result is converted to a binary code. In this application the user has to keep the reference voltage stable during the conversion cycle.

Oscillator

//Turns on and off a LED ,when pressings button attach to pin12
/**********************************/
const int keyPin = 12; //the number of the key pin
const int ledPin = 13;//the number of the led pin
/**********************************/
void setup()
{
  pinMode(keyPin,INPUT);//initialize the key pin as input 
  pinMode(ledPin,OUTPUT);//initialize the led pin as output
}
/**********************************/
void loop()
{
  //read the state of the key value
  //and check if the kye is pressed
  //if it is,the state is HIGH 
  if(digitalRead(keyPin) ==HIGH )
  {
    digitalWrite(ledPin,HIGH);//turn on the led
  }
  else
  {
    digitalWrite(ledPin,LOW);//turn off the led
  }
}
/************************************/

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