diff --git a/utils/Makefile b/utils/Makefile
index d434363..9a17eac 100644
--- a/utils/Makefile
+++ b/utils/Makefile
@@ -46,11 +46,13 @@ BINS=\
  BACK16M\
  BACKZX2\
  BACKZXD\
+ BACKZX3\
  BACKUP\
  CORCLEAN\
  COREBIOS\
  ZX1\
  ZX3\
+ BIT\
  DATE\
  RTCST\
  RTC.SYS\
@@ -59,6 +61,7 @@ BINS=\
  UPGR16M\
  UPGRZX2\
  UPGRZXD\
+ UPGRZX3\
  UPGRADE\
  ZXUNOCFG
 
@@ -89,7 +92,7 @@ build/BACKZX2: $(srcdir)/back32m.asm\
  $(INCLUDEDIR)/rdflsh.inc\
  $(INCLUDEDIR)/rst28.inc\
  | build
-	echo ' define zxdos 1' >back32m.def
+	echo ' define extension "2"' >back32m.def
 	$(AS) $(AFLAGS) --raw=$@ $<
 	rm -f back32m.def
 
@@ -100,7 +103,18 @@ build/BACKZXD: $(srcdir)/back32m.asm\
  $(INCLUDEDIR)/rdflsh.inc\
  $(INCLUDEDIR)/rst28.inc\
  | build
-	echo ' define zxdos 0' >back32m.def
+	echo ' define extension "D"' >back32m.def
+	$(AS) $(AFLAGS) --raw=$@ $<
+	rm -f back32m.def
+
+build/BACKZX3: $(srcdir)/back32m.asm\
+ $(INCLUDEDIR)/zxuno.def\
+ $(INCLUDEDIR)/esxdos.def\
+ $(INCLUDEDIR)/Print.inc\
+ $(INCLUDEDIR)/rdflsh.inc\
+ $(INCLUDEDIR)/rst28.inc\
+ | build
+	echo ' define extension "3"' >back32m.def
 	$(AS) $(AFLAGS) --raw=$@ $<
 	rm -f back32m.def
 
@@ -167,7 +181,7 @@ build/UPGRZX2: $(srcdir)/upgr32m.asm\
  $(INCLUDEDIR)/wrflsh.inc\
  $(INCLUDEDIR)/rst28.inc\
  | build
-	echo ' define zxdos 1' >upgr32m.def
+	echo ' define extension "2"' >upgr32m.def
 	$(AS) $(AFLAGS) --raw=$@ $<
 	rm -f upgr32m.def
 
@@ -178,7 +192,18 @@ build/UPGRZXD: $(srcdir)/upgr32m.asm\
  $(INCLUDEDIR)/wrflsh.inc\
  $(INCLUDEDIR)/rst28.inc\
  | build
-	echo ' define zxdos 0' >upgr32m.def
+	echo ' define extension "D"' >upgr32m.def
+	$(AS) $(AFLAGS) --raw=$@ $<
+	rm -f upgr32m.def
+
+build/UPGRZX3: $(srcdir)/upgr32m.asm\
+ $(INCLUDEDIR)/zxuno.def\
+ $(INCLUDEDIR)/esxdos.def\
+ $(INCLUDEDIR)/Print.inc\
+ $(INCLUDEDIR)/wrflsh.inc\
+ $(INCLUDEDIR)/rst28.inc\
+ | build
+	echo ' define extension "3"' >upgr32m.def
 	$(AS) $(AFLAGS) --raw=$@ $<
 	rm -f upgr32m.def
 
@@ -209,6 +234,12 @@ build/ZX3: $(srcdir)/zx3.asm\
  | build
 	$(AS) $(AFLAGS) --raw=$@ $<
 
+build/BIT: $(srcdir)/bit.asm\
+ $(INCLUDEDIR)/zxuno.def\
+ $(INCLUDEDIR)/esxdos.def\
+ | build
+	$(AS) $(AFLAGS) --raw=$@ $<
+
 build/DATE: $(srcdir)/date.asm\
  $(INCLUDEDIR)/zxuno.def\
  $(INCLUDEDIR)/esxdos.def\
diff --git a/utils/back32m.asm b/utils/back32m.asm
index 6de6b6c..0d1bdd9 100644
--- a/utils/back32m.asm
+++ b/utils/back32m.asm
@@ -26,24 +26,12 @@
 ; Compatible compilers:
 ;   SjAsmPlus, <https://github.com/z00m128/sjasmplus>
 
-                ; definition of "zxdos" flag
                 include back32m.def
-
-;             IF zxdos=1
-;               output  BACKZX2
-;             ELSE
-;               output  BACKZXD
-;             ENDIF
-
                 include zxuno.def
                 include esxdos.def
 
-        define  VERSION "0.1.1"
-              IF zxdos=1
-        define  FLASH_FILE "FLASH_32.ZX2"
-              ELSE
-        define  FLASH_FILE "FLASH_32.ZXD"
-              ENDIF
+        define  VERSION "0.1.2"
+        define  FLASH_FILE "FLASH_32.ZX", extension
 
                 org     $2000           ; comienzo de la ejecución de los comandos ESXDOS
 
diff --git a/utils/upgr32m.asm b/utils/upgr32m.asm
index 0d03600..45484b1 100644
--- a/utils/upgr32m.asm
+++ b/utils/upgr32m.asm
@@ -23,24 +23,12 @@
 ; Compatible compilers:
 ;   SjAsmPlus, <https://github.com/z00m128/sjasmplus>
 
-                ; definition of "zxdos" flag
                 include upgr32m.def
-
-;             IF zxdos=1
-;               output  UPGRZX2
-;             ELSE
-;               output  UPGRZXD
-;             ENDIF
-
                 include zxuno.def
                 include esxdos.def
 
-        define  VERSION "0.1.1"
-              IF zxdos=1
-        define  FLASH_FILE "FLASH_32.ZX2"
-              ELSE
-        define  FLASH_FILE "FLASH_32.ZXD"
-              ENDIF
+        define  VERSION "0.1.2"
+        define  FLASH_FILE "FLASH_32.ZX", extension
 
                 org     $2000           ; comienzo de la ejecución de los comandos ESXDOS