diff --git a/README.md b/README.md
index 74ba657..687eb93 100644
--- a/README.md
+++ b/README.md
@@ -19,6 +19,10 @@ The library lets you register listeners (callback functions) to wait for (1) any
 a particular frame Type, or (3) a specific message ID. This  high-level API lets you 
 easily implement various async communication patterns.
 
+TinyFrame is re-entrant and supports creating multiple instances with the limitation
+that their structure (field sizes and checksum type) must be the same. There is a support
+for adding multi-threaded access to a shared instance using a mutex (via a callback stub).
+
 ## Frame structure
 
 All fields in the message frame have a configurable size (see the top of the header file).
@@ -49,7 +53,9 @@ DATA_CKSUM .. checksum, implemented as XOR of all preceding bytes in the message
 
 - All TinyFrame functions, typedefs and macros start with the `TF_` prefix.
 - Both peers must include the library with the same parameters (configured at the top of the header file)
-- Start by calling `TF_Init()` with `TF_MASTER` or `TF_SLAVE` as the argument
+- Start by calling `TF_Init()` with `TF_MASTER` or `TF_SLAVE` as the argument. This creates a handle.
+  Use `TF_InitStatic()` to avoid the use of malloc(). If multiple instances are used, you can tag them 
+  using the `tf.userdata` / `tf.usertag` field.
 - Implement `TF_WriteImpl()` - declared at the bottom of the header file as `extern`.
   This function is used by `TF_Send()` and others to write bytes to your UART (or other physical layer).
   A frame can be sent in it's entirety, or in multiple parts, depending on its size.
diff --git a/TinyFrame.c b/TinyFrame.c
index 36baaa3..42c05d1 100644
--- a/TinyFrame.c
+++ b/TinyFrame.c
@@ -151,8 +151,12 @@ void _TF_FN TF_InitStatic(TinyFrame *tf, TF_Peer peer_bit)
 
     // Zero it out, keeping user config
     uint32_t usertag = tf->usertag;
+    void * userdata = tf->userdata;
+
     memset(tf, 0, sizeof(struct TinyFrame_));
+
     tf->usertag = usertag;
+    tf->userdata = userdata;
 
     tf->peer_bit = peer_bit;
 }
diff --git a/TinyFrame.h b/TinyFrame.h
index 4bb5551..43eb016 100644
--- a/TinyFrame.h
+++ b/TinyFrame.h
@@ -10,7 +10,7 @@
  * Upstream URL: https://github.com/MightyPork/TinyFrame
  */
 
-#define TF_VERSION "1.2.0"
+#define TF_VERSION "2.0.0"
 
 //---------------------------------------------------------------------------
 #include <stdint.h>  // for uint8_t etc
@@ -168,11 +168,8 @@ struct TF_GenericListener_ {
  */
 struct TinyFrame_ {
     /* Public user data */
-    union {
-        // choice between two representations
-        void *userdata;
-        uint32_t usertag;
-    };
+    void *userdata;
+    uint32_t usertag;
 
     // --- the rest of the struct is internal, do not access directly ---