diff --git a/README.md b/README.md
index 0925158..be75bcf 100644
--- a/README.md
+++ b/README.md
@@ -20,7 +20,7 @@ The main goal is to use modern sensors (mainly [I2C](https://github.com/orgua/iL
 - **DS2890 Single channel digital potentiometer - extended to 1-4 CH**
 
 ### Features:
-- supports up to 32 slaves (8 is standard setting), adjust ONEWIRESLAVE_LIMIT in OneWireHub.h to safe some RAM
+- supports up to 32 slaves (8 is standard setting), adjust ONEWIRESLAVE_LIMIT in OneWireHub.h to safe RAM & program space
 - hot-plug slaves as needed
 - cleaner, faster code with c++11 features (requires arduino sw 1.6.x or higher)
    - use of constexpr instead of #define for better compiler-messages
@@ -31,10 +31,10 @@ The main goal is to use modern sensors (mainly [I2C](https://github.com/orgua/iL
 - good documentation, numerous examples, easy interface for hub and sensors
 
 ### Recent development (latest at the top): 
-- rework of error system, slaves can raise errors now
+- rework of error system, switch to enum, slaves can raise errors now & there is only one Block using Serial
 - rework of the whole timings, if needed you can configure overdrive speed (arduino uno would probably be to slow)
 - bug fix: non conformal behaviour as a onewire-slave (hopefully)
-- raise the maximal slave limit from 8 to 32, takes ~100b extra program-space
+- raise the maximal slave limit from 8 to 32, code adapts via variable dataTypes
 - open up for a lot more platforms with "platform.h" (taken from onewire-lib)
 - fix bug: open-drain violation on slave side
 - per-bit-CRC16 with sendAndCRC16() and sendAndCRC16() for load-balancing, 900ns/bit instead of 7µs/byte on Atmega328@16MHz
diff --git a/src/OneWireHub.cpp b/src/OneWireHub.cpp
index 83da91e..79d2853 100644
--- a/src/OneWireHub.cpp
+++ b/src/OneWireHub.cpp
@@ -43,6 +43,9 @@ uint8_t OneWireHub::attach(OneWireItem &sensor)
         }
     }
 
+    if (position == 255)
+        return 255;
+
     slave_list[position] = &sensor;
     slave_count++;
     buildIDTree();
@@ -81,9 +84,9 @@ bool    OneWireHub::detach(const uint8_t slave_number)
 
 // just look through each bit of each ID and build a tree, so there are n=slaveCount decision-points
 // trade-off: more online calculation, but @4Slave 16byte storage instead of 3*256 byte
-uint8_t OneWireHub::getNrOfFirstBitSet(const uint32_t mask)
+uint8_t OneWireHub::getNrOfFirstBitSet(const mask_t mask)
 {
-    uint32_t _mask = mask;
+    mask_t _mask = mask;
     for (uint8_t i = 0; i < ONEWIRESLAVE_LIMIT; ++i)
     {
         if (_mask & 1)  return i;
@@ -95,7 +98,7 @@ uint8_t OneWireHub::getNrOfFirstBitSet(const uint32_t mask)
 // gone through the address, store this result
 uint8_t OneWireHub::getNrOfFirstFreeIDTreeElement(void)
 {
-    for (uint8_t i = 0; i < ONEWIRETREE_SIZE; ++i)
+    for (uint8_t i = 0; i < ONEWIRE_TREE_SIZE; ++i)
         if (idTree[i].id_position == 255)
             return i;
     return 0;
@@ -104,8 +107,8 @@ uint8_t OneWireHub::getNrOfFirstFreeIDTreeElement(void)
 // initial FN to build the ID-Tree
 uint8_t OneWireHub::buildIDTree(void)
 {
-    uint32_t mask_slaves = 0;
-    uint32_t bit_mask    = 0x01;
+    mask_t mask_slaves = 0;
+    mask_t bit_mask    = 0x01;
 
     // build mask
     for (uint8_t i = 0; i< ONEWIRESLAVE_LIMIT; ++i)
@@ -114,7 +117,7 @@ uint8_t OneWireHub::buildIDTree(void)
         bit_mask <<= 1;
     }
 
-    for (uint8_t i = 0; i< ONEWIRETREE_SIZE; ++i)
+    for (uint8_t i = 0; i< ONEWIRE_TREE_SIZE; ++i)
         idTree[i].id_position    = 255;
 
     // begin with root-element
@@ -124,17 +127,17 @@ uint8_t OneWireHub::buildIDTree(void)
 }
 
 // returns the branch that this iteration has worked on
-uint8_t OneWireHub::buildIDTree(uint8_t position_IDBit, const uint32_t mask_slaves)
+uint8_t OneWireHub::buildIDTree(uint8_t position_IDBit, const mask_t mask_slaves)
 {
     if (!mask_slaves) return (255);
 
     while (position_IDBit < 64)
     {
-        uint32_t mask_pos = 0;
-        uint32_t mask_neg = 0;
+        mask_t mask_pos = 0;
+        mask_t mask_neg = 0;
         const uint8_t pos_byte = (position_IDBit >> 3);
         const uint8_t mask_bit = (static_cast<uint8_t>(1) << (position_IDBit & (7)));
-        uint32_t mask_id = 1;
+        mask_t mask_id = 1;
 
         // search through all active slaves
         for (uint8_t id = 0; id < ONEWIRESLAVE_LIMIT; ++id)
@@ -312,7 +315,7 @@ bool OneWireHub::search(void)
         {
             sendBit(false);
             sendBit(false);
-            uint8_t bit_recv = recvBit();
+            const bool bit_recv = recvBit();
             if (_error != Error::NO_ERROR) return false;
 
             // switch to next junction
@@ -331,7 +334,7 @@ bool OneWireHub::search(void)
         {
             const uint8_t pos_byte = (position_IDBit >> 3);
             const uint8_t mask_bit = (static_cast<uint8_t>(1) << (position_IDBit & (7)));
-            uint8_t bit_send, bit_recv;
+            bool bit_send;
 
             if (slave_list[active_slave]->ID[pos_byte] & mask_bit)
             {
@@ -346,7 +349,7 @@ bool OneWireHub::search(void)
                 sendBit(true);
             }
 
-            bit_recv = recvBit();
+            const bool bit_recv = recvBit();
             if (_error != Error::NO_ERROR)  return false;
 
             if (bit_send != bit_recv)
diff --git a/src/OneWireHub.h b/src/OneWireHub.h
index 0b518e9..8663667 100644
--- a/src/OneWireHub.h
+++ b/src/OneWireHub.h
@@ -8,12 +8,23 @@
 #define USE_SERIAL_DEBUG 0 // give debug messages when printError() is called
 // INFO: had to go with a define because some compilers use constexpr as simple const --> massive problems
 
+#define HUB_SLAVE_LIMIT 8 // set the limit of the hub HERE
+
+
+#ifndef HUB_SLAVE_LIMIT
+#error "Slavelimit not defined (why?)"
+#elif (HUB_SLAVE_LIMIT > 32)
+#error "Slavelimit is set to high (32)"
+#elif (HUB_SLAVE_LIMIT > 16)
+using mask_t = uint32_t;
+#elif (HUB_SLAVE_LIMIT > 8)
+using mask_t = uint16_t;
+#elif (HUB_SLAVE_LIMIT > 0)
+using mask_t = uint8_t;
+#else
+#error "Slavelimit is set to zero (why?)"
+#endif
 
-// TODO: rework this whole system
-// - cleaner timing-system throughout the lib (raw tick-counter of micros()?)
-// - offer strict and relaxed timing option (if master is also emulated)
-// - offer interruptable read / write OPs
-// - safe timestamp of last HIGH, LOW state?
 
 enum class Error : uint8_t {
     NO_ERROR                   = 0,
@@ -38,8 +49,8 @@ class OneWireHub
 {
 private:
 
-    static constexpr uint8_t ONEWIRESLAVE_LIMIT                 = 8; // 32 is max at the moment
-    static constexpr uint8_t ONEWIRETREE_SIZE                   = 2*ONEWIRESLAVE_LIMIT - 1;
+    static constexpr uint8_t ONEWIRESLAVE_LIMIT                 = HUB_SLAVE_LIMIT;
+    static constexpr uint8_t ONEWIRE_TREE_SIZE                  = 2*ONEWIRESLAVE_LIMIT - 1;
 
 
     /// the following TIME-values are in us and are taken from the ds2408 datasheet
@@ -89,12 +100,12 @@ class OneWireHub
         uint8_t id_position;    // where does the algorithm has to look for a junction
         uint8_t got_zero;        // if 0 switch to which tree branch
         uint8_t got_one;         // if 1 switch to which tree branch
-    } idTree[ONEWIRETREE_SIZE];
+    } idTree[ONEWIRE_TREE_SIZE];
 
     uint8_t buildIDTree(void);
-    uint8_t buildIDTree(uint8_t position_IDBit, const uint32_t slave_mask);
+    uint8_t buildIDTree(uint8_t position_IDBit, const mask_t slave_mask);
 
-    uint8_t getNrOfFirstBitSet(const uint32_t mask);
+    uint8_t getNrOfFirstBitSet(const mask_t mask);
     uint8_t getNrOfFirstFreeIDTreeElement(void);
 
     bool checkReset(uint16_t timeout_us);