diff --git a/README.md b/README.md
index e3543c7..455f8ed 100644
--- a/README.md
+++ b/README.md
@@ -1,7 +1,9 @@
 # RFM69-Library-AVR #
-Original library is written for arduino by [LowPowerLab](https://github.com/LowPowerLab/RFM69). This is C ported version for AVR microcontrollers.
+Original library is written for arduino by [LowPowerLab](https://github.com/LowPowerLab/RFM69).
+The AVR based library can be found: https://github.com/nayem-cosmic/RFM69-Library-AVR
 
-Tested on ATmega64, ATmega328, ATtiny84.
+The AVR based library has been modified for STM32 compatibility.
+Tested on STM32F103C8.
 
 </br>
 
@@ -17,6 +19,37 @@ Tested on ATmega64, ATmega328, ATtiny84.
 
 </br>
 
+## Functions need to be implemented: ##
+
+void spi_transfer_sync(uint8_t *dataout, uint8_t *datain, uint8_t len);
+Shift full array through target device.
+
+void spi_transmit_sync(uint8_t *dataout, uint8_t len);
+Shift full array to target device without receiving any byte.
+ 
+uint8_t spi_fast_shift(uint8_t data);
+Clocks only one byte to target device and returns the received one.
+
+uint32_t millis();
+Return with the millisecs. It can be done by a timer or by the ticks.
+
+void select();
+Enable SPI transfer. (Negated logic - Pulled LOW means selection)
+
+void unselect();
+Disable SPI transfer. (Negated logic - Pulled HIGH means unselection)
+
+void cli();
+Disable the interrupt of the RFM69 pin. 
+
+void sei();
+Enable the interrupt of the RFM69 pin. 
+
+void reset_rfm69(void); OPTIONAL
+Reset the RFM69 modul via its reset pin.
+
+These functions have to be externed, to make possible the function call by the library.
+
 ## Function Description: ##
 
 1.	**rfm69_init(*uint16_t freqBand, uint8_t nodeID, uint8_t networkID*):** Initializes rfm69 module. This function is called at the beginning of the program. Initializes IDs, modes etc. It takes three parameters. First one freqBand. You have to choose among 315, 433, 868 and 915. These specifies frequency in MHz. nodeID is analogues to device ID. Each RF module will have unique nodeID. Value must be within 0 to 255. Then comes notworkID. Say, a system has 5 rf modules to communicate with each other. All the modules must be in same networkID . networkID value range 0~255.