diff --git a/sbapack/dec.py b/sbapack/dec.py
index 685e406..2c4f447 100644
--- a/sbapack/dec.py
+++ b/sbapack/dec.py
@@ -20,7 +20,7 @@
 # Default values
 # ------------------------------------------------------------------------------
 
-VERSION = "3.03.06"
+VERSION = "3.03.06mosfix1"
 DEF_ENV = "SBASM"
 ERRLVL_OK = 0       # No errors
 ERRLVL_PASS1 = 1    # Errors found during pass 1
@@ -37,6 +37,7 @@
 COMMENT1 = ";*#@"       # Legal comment delimiters on beginning of the line
 COMMENT2 = ";"          # Legal comment delimiters anywhere else on the line
 EOL = '\n'              # System dependant end of line character
+XOFF = '\x13'           # XOFF char 0x13 = dec(19) = ctrl+S
 MAX8 = (1 << 8)-1       # Max value for 8 bit numbers
 MAX16 = (1 << 16)-1     # Max value for 16 bit numbers
 MAX32 = (1 << 32)-1     # Max value for 32 bit numbers
@@ -96,6 +97,7 @@ class Struct:       # General data structure class
 Asm.Code_Tfile = None     # File handle for code target file
 Asm.Code_Tbuffer = []     # Line buffer for code target file
 Asm.Code_Tformat = ''     # Code file's format
+Asm.Code_TformatMOS_records  = 0 # static record/line counter for TformatMOS()
 Asm.Code_Tfunc = None     # Indirect function handler
 Asm.Code_Tlength = 0      # Wanted target record length
 Asm.Code_Twrap = False    # Set if wrap warning already given
diff --git a/sbapack/target.py b/sbapack/target.py
index ec05ec4..7cd3194 100644
--- a/sbapack/target.py
+++ b/sbapack/target.py
@@ -421,9 +421,13 @@ def TformatMOS(buffer, memory, last=False):
 
     """
     Format a MOS technology target file.
+    Implement MOS format from here:
+    https://archive.org/details/KIM-1_Users_Manual/page/n98/mode/1up
+    https://srecord.sourceforge.net/man/man5/srec_mos_tech.5.html
     """
 
     if len(buffer) > 0:
+        dec.Asm.Code_TformatMOS_records += 1    # count record/line
         address = buffer[0]
         length = len(buffer) - 1
         checksum = length + ((address >> 8) & 0xFF) + (address & 0xFF)
@@ -444,7 +448,22 @@ def TformatMOS(buffer, memory, last=False):
         line = ''
 
     if last:
-        line = line + ';00' + dec.EOL
+        # Checked KIM-ROM how last line is processed
+        # after ';' it read the length and the address (as usual including calc the checksum)
+        # For lastline length=0 then only the checksum of address counts
+        # no more data read because of length=0
+        # next 2 byte are read and compared against the checksum (as usual nothing special except length=0 does not count)
+        # !!! for the first 255 lines address and checksum have the same value
+        # example: ";0000090009"  or ";000230023" but ";0001230024"
+        # checksum == bad  => print from offset 0x11 to TOP "\r ERR\r KIM\r\n" + 6 zero bytes
+        # checksum == good => print from offset 0x0c to TOP       "\r KIM\r\n" + 6 zero bytes
+        # It will not expect or read further data like XOFF or EOL
+        # after print it will directly "JMP START" for further processing
+        # The XOFF and EOL are added to not confuse editor
+        line = line + ';00'     # length = 0
+        address = dec.Asm.Code_TformatMOS_records
+        checksum = ((address >> 8) & 0xFF) + (address & 0xFF)   # length = 0
+        line = line + ToHex(address, 2) + ToHex(checksum, 2) + dec.XOFF + dec.EOL
 
     return line.upper()