user8134: I am trying to send and receive data using I2C between an Arduino Uno and an ATTiny85. The Arduino Uno is using the Wire library. The ATTiny85 is using the TinyWire library and is programmed (and powered) using the Sparkfun Tiny AVR Programmer.
I am not receiving any data.
Arduino Uno I2C master code
#include <Wire.h>

#define SLAVE_ADDR 0x50

void setup()
{
  Wire.begin();
  Serial.begin(9600);
}

void loop()
{
  Wire.requestFrom(SLAVE_ADDR, 1);

  while(Wire.available())
  { 
    byte byteReceived = Wire.read();
    Serial.println(byteReceived, DEC);
  }
}

ATTiny85 I2C slave code
#include "TinyWireS.h"

#define SLAVE_ADDR 0x50

void setup()
{
  TinyWireS.begin(SLAVE_ADDR);
  TinyWireS.onRequest(requestEvent);
}


void loop()
{
}

void requestEvent()
{
  byte byteToSend = 23;
  TinyWireS.send(byteToSend);
}


user10794: I modified your Uno sketch slightly to add a delay:
#include <Wire.h>

#define SLAVE_ADDR 0x50

void setup()
{
  Wire.begin();
  Serial.begin(9600);
}

void loop()
{
  Wire.requestFrom(SLAVE_ADDR, 1);

  if (Wire.available())
  { 
    byte byteReceived = Wire.read();
    Serial.println(byteReceived, DEC);
  }

 delay (1000);
}

Upon testing, it worked perfectly!
23
23
23
23
23
23
23
23
23
23
23
23

I suggest a wiring error. Check you have:
Uno    ATtiny85
--------------------
A4      pin 5  (SDA)
A5      pin 7  (SCL)
+5V     pin 8
Gnd     pin 4


8134: <p>I am trying to send and receive data using I2C between an Arduino Uno and an ATTiny85. The Arduino Uno is using the Wire library. The ATTiny85 is using the TinyWire library and is programmed (and powered) using the Sparkfun Tiny AVR Programmer.</p>

<p>I am not receiving any data.</p>

<p>Arduino Uno I2C master code</p>

<pre><code>#include &lt;Wire.h&gt;

#define SLAVE_ADDR 0x50

void setup()
{
  Wire.begin();
  Serial.begin(9600);
}

void loop()
{
  Wire.requestFrom(SLAVE_ADDR, 1);

  while(Wire.available())
  { 
    byte byteReceived = Wire.read();
    Serial.println(byteReceived, DEC);
  }
}
</code></pre>

<p>ATTiny85 I2C slave code</p>

<pre><code>#include "TinyWireS.h"

#define SLAVE_ADDR 0x50

void setup()
{
  TinyWireS.begin(SLAVE_ADDR);
  TinyWireS.onRequest(requestEvent);
}


void loop()
{
}

void requestEvent()
{
  byte byteToSend = 23;
  TinyWireS.send(byteToSend);
}
</code></pre>
 10794: 

<p>I modified your Uno sketch slightly to add a delay:</p>

<pre class="lang-C++ prettyprint-override"><code>#include &lt;Wire.h&gt;

#define SLAVE_ADDR 0x50

void setup()
{
  Wire.begin();
  Serial.begin(9600);
}

void loop()
{
  Wire.requestFrom(SLAVE_ADDR, 1);

  if (Wire.available())
  { 
    byte byteReceived = Wire.read();
    Serial.println(byteReceived, DEC);
  }

 delay (1000);
}
</code></pre>

<p>Upon testing, it worked perfectly!</p>



<pre class="lang-none prettyprint-override"><code>23
23
23
23
23
23
23
23
23
23
23
23
</code></pre>

<p>I suggest a wiring error. Check you have:</p>

<pre class="lang-none prettyprint-override"><code>Uno    ATtiny85
--------------------
A4      pin 5  (SDA)
A5      pin 7  (SCL)
+5V     pin 8
Gnd     pin 4
</code></pre>
