diff --git a/sdk/src/tools/rcs.c b/sdk/src/tools/rcs.c
new file mode 100644
index 0000000..d632cbd
--- /dev/null
+++ b/sdk/src/tools/rcs.c
@@ -0,0 +1,100 @@
+/*
+ * rcs - SCR filter to RCS (and inverse).
+ *
+ * Copyright (C) 2013, 2021 Antonio Villena
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, version 3.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <https://www.gnu.org/licenses/>.
+ *
+ * SPDX-FileCopyrightText: Copyright (C) 2013, 2021 Antonio Villena
+ *
+ * SPDX-License-Identifier: GPL-3.0-only
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+
+#define PROGRAM "rcs"
+#define DESCRIPTION "SCR filter to RCS (and inverse)."
+#define VERSION "1.03 (18 Jan 2013)"
+#define COPYRIGHT "Copyright (C) 2013, 2021 Antonio Villena"
+#define LICENSE \
+"This program is free software: you can redistribute it and/or modify\n" \
+"it under the terms of the GNU General Public License as published by\n" \
+"the Free Software Foundation, version 3."
+#define HOMEPAGE "https://github.com/zxdos/zxuno/"
+
+void show_help() {
+  printf(
+    PROGRAM " version " VERSION " - " DESCRIPTION "\n"
+    COPYRIGHT "\n"
+    LICENSE "\n"
+    "Home page: " HOMEPAGE "\n"
+    "\n"
+    "Usage:\n"
+    "  " PROGRAM " [-i] <input_file> <output_file>\n"
+    "\n"
+    "  -i             Inverse filter (RCS to SCR), optional\n"
+    "  <input_file>   Input file to filter\n"
+    "  <output_file>  Generated output file\n"
+    "\n"
+    "All parameters are mandatory except `-i'.\n"
+  );
+}
+
+int scr2rcs( int i ){ return i&0x1800 | i<<8&0x700 | i<<2&0xe0 | i>>6&0x1f;  }
+int rcs2scr( int i ){ return i&0x1800 | i>>8&7     | i>>2&0x38 | i<<6&0x7c0; }
+int main(int argc, char* argv[]){
+  unsigned char *mem= (unsigned char *) malloc (0x1b00);
+  int tmp, last, j, k;
+  FILE *fi, *fo;
+  if( argc==1 )
+    show_help(),
+    exit(0);
+  int (*func)(int)= &scr2rcs;
+  if( argv[1][0] == '-' )
+    func= &rcs2scr, argv++, argc--;
+  if( argc!=3 )
+    printf("Invalid number of parameters\n"),
+    exit(-1);
+  fi= fopen(argv[1], "rb");
+  if( !fi )
+    printf("Input file not found: %s\n", argv[1]),
+    exit(-1);
+  fo= fopen(argv[2], "wb+");
+  if( !fo )
+    printf("Cannot create output file: %s\n", argv[2]),
+    exit(-1);
+  fread(mem, 1, 0x1b01, fi);
+  if( ftell(fi) != 0x1b00 )
+    printf("Input file size must be 6912 bytes\n"),
+    exit(-1);
+  for ( int i= 0; i<0x1800; i++ ){
+    k= j= i;
+    do
+      last= j,
+      j= func(j),
+      k<j && (k= j, j= i);
+    while( j != i );
+    if( k==i ){
+      tmp= mem[j];
+      do
+        k= func(j),
+        mem[j]= mem[k],
+        j= k;
+      while( j != i );
+      mem[last]= tmp;
+    }
+  }
+  fwrite(mem, 1, 0x1b00, fo);
+  printf("File `%s' successfully created\n",argv[2]);
+}