diff --git a/lib/onewire_slave.c b/lib/onewire_slave.c
index f712a0b..bf5ab0d 100644
--- a/lib/onewire_slave.c
+++ b/lib/onewire_slave.c
@@ -154,35 +154,43 @@ void onewire_slave_setup(uint8_t family, uint64_t serial)
 	nvic_enable_irq(NVIC_EXTI_IRQ(ONEWIRE_SLAVE_PIN)); // enable interrupt
 }
 
-void onewire_slave_function_read(uint8_t* data, uint32_t bits)
+bool onewire_slave_function_read(uint8_t* data, size_t size)
 {
-	if (NULL==data || 0==bits) { // verify input
-		return;
+	if (NULL==data || 0==size) { // verify input
+		return false;
+	}
+	if (UINT32_MAX/8<size) { // too many bits to transfer
+		return false;
 	}
 	if (onewire_slave_state!=ONEWIRE_STATE_FUNCTION_DATA) { // not in the right state to transfer data
-		return;
+		return false;
 	}
 	onewire_slave_transfer_data = data; // save buffer to write to
-	onewire_slave_transfer_bits = bits; // number of bits to read
+	onewire_slave_transfer_bits = size*8; // number of bits to read
 	onewire_slave_transfer_complete = false; // reset state
 	bits_bit = 0; // reset number of bits read
 	onewire_slave_state = ONEWIRE_STATE_FUNCTION_READ; // read data
+	return true;
 }
 
-void onewire_slave_function_write(uint8_t* data, uint32_t bits)
+bool onewire_slave_function_write(const uint8_t* data, size_t size)
 {
-	if (NULL==data || 0==bits) { // verify input
-		return;
+	if (NULL==data || 0==size) { // verify input
+		return false;
 	}
 	if (onewire_slave_state!=ONEWIRE_STATE_FUNCTION_DATA) { // not in the right state to transfer data
-		return;
+		return false;
 	}
-	onewire_slave_transfer_data = data; // save buffer to read from
-	onewire_slave_transfer_bits = bits; // number of bits to write
+	if (UINT32_MAX/8<size) { // too many bits to transfer
+		return false;
+	}
+	onewire_slave_transfer_data = (uint8_t*)data; // save buffer to read from
+	onewire_slave_transfer_bits = size*8; // number of bits to write
 	onewire_slave_transfer_complete = false; // reset state
 	bits_bit = 0; // reset number of bits written
 	bits_buffer = onewire_slave_transfer_data[0]; // prepare byte to write
 	onewire_slave_state = ONEWIRE_STATE_FUNCTION_WRITE; // write data
+	return true;
 }
 
 /** interrupt service routine called when 1-Wire signal changes */
diff --git a/lib/onewire_slave.h b/lib/onewire_slave.h
index 0fe9d32..af05eb4 100644
--- a/lib/onewire_slave.h
+++ b/lib/onewire_slave.h
@@ -39,13 +39,15 @@ extern volatile bool onewire_slave_transfer_complete;
 void onewire_slave_setup(uint8_t family, uint64_t serial);
 /** read data from master
  *  @param[out] data buffer to save read bits
- *  @param[in] bits number of bits to read
+ *  @param[in] size number of bytes to read
+ *  @return if transfer initialization succeeded
  *  @note onewire_slave_transfer_complete is set when transfer is completed
  */
-void onewire_slave_function_read(uint8_t* data, uint32_t bits);
+bool onewire_slave_function_read(uint8_t* data, size_t size);
 /** write data to master
  *  @param[in] data data to write
- *  @param[in] bits number of bits to write
+ *  @param[in] size number of bytes to write
+ *  @return if transfer initialization succeeded
  *  @note onewire_slave_transfer_complete is set when transfer is completed
  */
-void onewire_slave_function_write(uint8_t* data, uint32_t bits);
+bool onewire_slave_function_write(const uint8_t* data, size_t size);