Update README.md

Author: budulinek

README.md

@@ -1,2 +1,37 @@
 # Arduino-Modbus-RTU---Modbus-TCP-UDP-Gateway
 Transparent gateway Modbus RTU <---> Modbus TCP / Modbus UDP for Arduino
+
+## Hardware
+* Arduino (Nano, Uno, possibly other)
+* W5500 Ethernet shield
+* MAX485 (or other RS485 TTL module)
+
+## Features
+* slaves are on the Modbus RTU side, masters are on the Modbus TCP or Modbus UDP side
+* supports up to 247 Modbus RTU slaves
+* supports Modbus UDP masters and up to 8 Modbus TCP masters connected at the same time
+* supports broadcast (slave address 0x00)
+* supports error codes (forwards error codes from slaves, sends its own error codes)
+* supports all Modbus function codes (incl. proprietary)
+* optimized queue for Modbus requests 
+  * queue will accept only one requests to a slave which is not responding
+  * requests to responding slaves are processed first
+
+## Connections
+  Arduino <-> MAX485
+  Tx1 <-> DI
+  Rx0 <-> RO
+  Pin 6 <-> DE,RE
+  
+## Settings
+* RS485 settings
+  * BAUD
+  * SERIAL_CONFIG   (sets data, parity, and stop bits)
+  * SERIAL_TIMEOUT  (timeout for Modbus RTU request)
+  * MAX_RETRY       (maximum number of retries)
+* TCP and UDP settings
+  * MAC, IP,  GATEWAY, SUBNET
+  * TCP_PORT        (local Modbus TCP port)
+  * ETH_MAX_RETRY   (maximum number of retries for sending UDP packet / TCP response)
+  * UDP_PORT        (OPTIONAL: local Modbus UDP port, defaults to Modbus TCP port)
+