--- stk500-orig.c	2011-09-15 15:37:04.000000000 +0100
+++ stk500.c	2013-12-06 22:45:30.000000000 +0000
@@ -689,14 +689,31 @@
 }
 
 
-static int stk500_loadaddr(PROGRAMMER * pgm, unsigned int addr)
+static int stk500_loadaddr(PROGRAMMER * pgm, unsigned int addr, char ext_addr)
 {
   unsigned char buf[16];
   int tries;
+  static unsigned char prev_ext_byte = 0xff; /* Ensures it is set first time */
+  unsigned char ext_byte;
 
   tries = 0;
  retry:
   tries++;
+
+  /* To support flash > 64K words the correct Extended Address Byte has to be programmed. Use cmnd-universal */
+  if (ext_addr) {
+    ext_byte = (addr >> 16) & 0xff;
+    if (ext_byte != prev_ext_byte) {
+      /* 'Load Extended Address Byte' 0x4d,0x00 see Atmel datasheets, 'Serial Programming Instructions' */
+      buf[0] = 0x4d;
+      buf[1] = 0x00;
+      buf[2] = ext_byte;
+      buf[3] = 0x00;
+      stk500_cmd(pgm, buf, buf);
+      prev_ext_byte = ext_byte;
+    }
+  }
+
   buf[0] = Cmnd_STK_LOAD_ADDRESS;
   buf[1] = addr & 0xff;
   buf[2] = (addr >> 8) & 0xff;
@@ -751,6 +768,7 @@
   unsigned int n;
   unsigned int i;
   int flash;
+  char use_ext_addr = 0;
 
   if (page_size == 0) {
     // MIB510 uses page size of 256 bytes
@@ -765,6 +783,9 @@
   if (strcmp(m->desc, "flash") == 0) {
     memtype = 'F';
     flash = 1;
+    /* To support flash > 128K (64K words) use an Extended Address Byte */
+    if (m->size > 131072)
+      use_ext_addr = 1;
   }
   else if (strcmp(m->desc, "eeprom") == 0) {
     memtype = 'E';
@@ -822,7 +843,7 @@
     tries = 0;
   retry:
     tries++;
-    stk500_loadaddr(pgm, addr/a_div);
+    stk500_loadaddr(pgm, addr/a_div, use_ext_addr);
 
     /* build command block and avoid multiple send commands as it leads to a crash
         of the silabs usb serial driver on mac os x */
@@ -895,9 +916,13 @@
   int tries;
   unsigned int n;
   int block_size;
+  char use_ext_addr = 0;
 
   if (strcmp(m->desc, "flash") == 0) {
     memtype = 'F';
+    /* To support flash > 128K (64K words) use an Extended Address Byte */
+    if (m->size > 131072)
+      use_ext_addr = 1;
   }
   else if (strcmp(m->desc, "eeprom") == 0) {
     memtype = 'E';
@@ -939,7 +964,7 @@
     tries = 0;
   retry:
     tries++;
-    stk500_loadaddr(pgm, addr/a_div);
+    stk500_loadaddr(pgm, addr/a_div, use_ext_addr);
     buf[0] = Cmnd_STK_READ_PAGE;
     buf[1] = (block_size >> 8) & 0xff;
     buf[2] = block_size & 0xff;