diff --git a/SoftRS485.cpp b/SoftRS485.cpp
index 1f7ed4f..32c43ba 100644
--- a/SoftRS485.cpp
+++ b/SoftRS485.cpp
@@ -12,11 +12,12 @@
 // Pins
 int _RO, _RE, _DE, _DI;
 
-const long _pulse_len = 1000;
-const long _break = _pulse_len * 20;
-boolean _line = LOW;     // current state of the transmission line
-long _last_flip = 0;     // timestamp since last flip of line state
-boolean _start = false;  // indicates whether a start bit shall be ignored
+const unsigned long _pulse_len = 1000;
+const unsigned long _break = _pulse_len * 20;
+
+unsigned long _last_flip = 0;     // timestamp of last flip of line state
+boolean _line = LOW;              // current state of the transmission line
+boolean _start = false;           // indicates whether a start bit shall be ignored
 
 // Receive vars
 byte _recv_msg[MSG_LEN]; // message buffer
@@ -25,9 +26,9 @@ int _pos = 0;            // character position within the buffer
 int _idx = 0;            // bit position within the current character
 
 // variables, that could be local, but are stored globally for speed optimization
-long _diff = 0;          // time difference between last flips
-long _now = 0;           // current time
-long _count = 0;         // helper for bit iteration
+unsigned long _diff = 0;          // time difference between last flips
+unsigned long _now = 0;           // current time
+unsigned long _count = 0;         // helper for bit iteration
 
 
 #if defined CONTROLLINO_MAXI
@@ -74,9 +75,9 @@ void interrupt485(){
             Serial.print(_line);
 #endif
             if (_idx == 8){                        // full byte received
-                if (_recv_msg[_pos] == 0x00){      // received byte is string terminator
+                if (_pos == MSG_LEN || _recv_msg[_pos] == 0x00){      // received byte is string terminator
                     _avail = true;                 // notify about complete transmission
-// TODO: prevent writing out of buffer boundaries!                    
+                    break;
                 }
                 _pos++;                            // advance to nect character of buffer
                 _idx=0;                            // start with first bit of that character