I keep receiving the following error in myATTiny85-Slave code below:

sketch_mar12a.ino: In function 'void setup()':

sketch_mar12a:19: error: 'class USI_TWI_S' has no member named 'onRequest'

I have downloaded TinyWireS and TinyWireS.h clearly has a public function onRequest. I opened the .ZIP file (downloaded from https://github.com/rambo/TinyWire) and drag-dropped TinyWireS folder into the Arduino libraries folder. This is how I install ALL libraries.

I am using Arduino 1.0.6

What am I doing wrong?

ATTiny85-Slave Code:

#include "TinyWireS.h"                  // wrapper class for I2C slave routines
#define I2C_SLAVE_ADDR  0x26            // i2c slave address (38)

byte t=10;

void setup()
   TinyWireS.begin(I2C_SLAVE_ADDR);      // init I2C Slave mode

void loop()

void requestEvent()

Arduino Uno-Master Code:

 #include <Wire.h>
 #define I2C_SLAVE_ADDR  0x26            // i2c slave address (38)

 void setup() 

 void loop() 
      byte num;

     // read 1 byte, from address 0x26
     Wire.requestFrom(I2C_SLAVE_ADDR, 1);

     while(Wire.available()) {
          num = Wire.read();
     Serial.print("num = ");
  • How did you install the library?
    – Gerben
    Mar 13, 2015 at 15:35
  • I opened the .ZIP file (downloaded from github.com/rambo/TinyWire) and drag-dropped TinyWireS folder into the Arduino libraries folder. This is how I install ALL libraries.
    – lucidgold
    Mar 13, 2015 at 18:52
  • you may need to include: TinyWireS_stop_check(); in your loop
    – diy_bloke
    Feb 18, 2016 at 11:56

1 Answer 1


I was able to compile your code "ATTiny85-Slave Code" without problems.

You can try to extract the contents of the ZIP archive (i.e. the library) directly to the directory where your sketch is stored. #include "TinyWireS.h" should then pick up that version.

You should also switch on verbose output for the compilation to have a look at the directory in which the code is compiled. Here you would find (at least in my older Arduino IDE version) copies of the included files. (/tmp/build... on Linux systems.) You can then make sure the proper version of the files is used.

You can also search your drives for other copies of TinyWireS.h.

  • Which version of Arduino IDE are you using? What board did you select?
    – lucidgold
    Mar 14, 2015 at 16:45
  • I am using Arduino IDE 1.0. It compiles with any board selection... Note that I did not install the Tiny hardware specs, but did a small hack in usiTwiSlace.c, declaring all missing symbols as ints. Mar 14, 2015 at 17:32

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