diff --git a/constants.h b/constants.h
new file mode 100644
index 0000000..9ecfdc9
--- /dev/null
+++ b/constants.h
@@ -0,0 +1,38 @@
+#pragma once
+#include "parser.h"
+
+void register_constants() {
+	parser_register_constant("ink_red", 0x00);
+	parser_register_constant("ink_lime", 0x01);
+	parser_register_constant("ink_blue", 0x02);
+	parser_register_constant("ink_magenta", 0x03);
+	parser_register_constant("ink_yellow", 0x04);
+	parser_register_constant("ink_cyan", 0x05);
+	parser_register_constant("ink_white", 0x06);
+	parser_register_constant("ink_black", 0x07);
+	parser_register_constant("ink_brown", 0x08);
+	parser_register_constant("ink_green", 0x09);
+	parser_register_constant("ink_navy", 0x0A);
+	parser_register_constant("ink_purple", 0x0B);
+	parser_register_constant("ink_gold", 0x0C);
+	parser_register_constant("ink_teal", 0x0D);
+	parser_register_constant("ink_gray", 0x0E);
+	parser_register_constant("ink_black2", 0x0F);
+
+	parser_register_constant("paper_red", 0x00);
+	parser_register_constant("paper_lime", 0x10);
+	parser_register_constant("paper_blue", 0x20);
+	parser_register_constant("paper_magenta", 0x30);
+	parser_register_constant("paper_yellow", 0x40);
+	parser_register_constant("paper_cyan", 0x50);
+	parser_register_constant("paper_white", 0x60);
+	parser_register_constant("paper_black", 0x70);
+	parser_register_constant("paper_brown", 0x80);
+	parser_register_constant("paper_green", 0x90);
+	parser_register_constant("paper_navy", 0xA0);
+	parser_register_constant("paper_purple", 0xB0);
+	parser_register_constant("paper_gold", 0xC0);
+	parser_register_constant("paper_teal", 0xD0);
+	parser_register_constant("paper_gray", 0xE0);
+	parser_register_constant("paper_black2", 0xF0);
+}
diff --git a/main.cpp b/main.cpp
index ac6f038..fc10df9 100644
--- a/main.cpp
+++ b/main.cpp
@@ -4,6 +4,35 @@
 #include "vdp.h"
 #include <SDL.h>
 
+#define BTN_ANY		0
+#define BTN_UP		1
+#define BTN_DOWN	2
+#define BTN_LEFT	3
+#define BTN_RIGHT	4
+#define BTN_A		5
+#define BTN_B		6
+#define BTN_MENU	7
+
+bool anykey = false;
+unsigned char data_in;
+
+void input_data_in(const unsigned char& value) {
+	data_in = value;
+}
+
+unsigned char input_data_out() {
+	const Uint8* keys = SDL_GetKeyboardState(nullptr);
+	switch (data_in) {
+	case BTN_ANY: return anykey; break;
+	case BTN_UP: return keys[SDL_SCANCODE_UP]; break;
+	case BTN_DOWN: return keys[SDL_SCANCODE_DOWN]; break;
+	case BTN_LEFT: return keys[SDL_SCANCODE_LEFT]; break;
+	case BTN_RIGHT: return keys[SDL_SCANCODE_RIGHT]; break;
+	case BTN_A: return keys[SDL_SCANCODE_RCTRL]; break;
+	case BTN_B: return keys[SDL_SCANCODE_RSHIFT]; break;
+	case BTN_MENU: return keys[SDL_SCANCODE_RETURN]; break;
+	};
+}
 
 int main(int argc, char** argv) {
 
@@ -11,22 +40,26 @@ int main(int argc, char** argv) {
 	vdp_init();
 	vm_register_out_port(10, vdp_data_out);
 	vm_register_out_port(11, vdp_cmd_out);
+	vm_register_out_port(20, input_data_in);
+	vm_register_in_port(21, input_data_out);
 
 	static bool should_quit = false;
 	static SDL_Event sdlEvent;
 	SDL_Scancode just_pressed;
 
+	//Uint32 ticks = SDL_GetTicks();
 	while (!should_quit) {
 		just_pressed = SDL_SCANCODE_UNKNOWN;
 		while (SDL_PollEvent(&sdlEvent)) {
 			if (sdlEvent.type == SDL_QUIT) { should_quit = true; break; }
 			else if (sdlEvent.type == SDL_KEYDOWN) {
-				//anyKey = true;
+				anykey = true;
 				just_pressed = sdlEvent.key.keysym.scancode;
 				if (sdlEvent.key.keysym.scancode == SDL_SCANCODE_ESCAPE) { should_quit = true; }
 			}
 		}
 		vm_step();
+		//if (SDL_GetTicks() - ticks >= 15) { vdp_flip(); ticks = SDL_GetTicks(); }
 	}
 
 	vdp_quit();
diff --git a/parser.cpp b/parser.cpp
index bc3b5a6..f3924f6 100644
--- a/parser.cpp
+++ b/parser.cpp
@@ -9,6 +9,7 @@
 #define MAX_LABELS				256
 #define MAX_EXTERNAL_FUNCTIONS	256
 #define MAX_IDENTIFIER_LENGTH	40
+#define MAX_CONSTANTS			256
 
 struct t_label {
 	char		name[MAX_IDENTIFIER_LENGTH];
@@ -33,6 +34,11 @@ struct t_string {
 	int			num_references = 1;
 };
 
+struct t_constant {
+	char		name[MAX_IDENTIFIER_LENGTH];
+	byte		value;
+};
+
 static byte* code; // [MAX_CODE_SIZE];
 static word codepos = 0;
 
@@ -57,6 +63,9 @@ static int num_strings = 0;
 
 static bool parser_finished = false;
 
+static t_constant constants[MAX_CONSTANTS];
+static int num_constants;
+
 /****************************************************************************************/
 /* GENERIC FUNCTIONS																	*/	
 /****************************************************************************************/
@@ -119,11 +128,27 @@ static int get_variable_index(const char* string, const int array_size = 1) {
 	else {
 		variables = newvar;
 	}
-	return newvar->index;
+	return newvar->index + 0xC000;
 }
 
 static bool is_variable_array() { return variable_is_array; }
 
+/****************************************************************************************/
+/* CONSTANT MANAGEMENT																	*/
+/****************************************************************************************/
+void parser_register_constant(const char* name, const unsigned char value) {
+	strcpy(constants[num_constants].name, name);
+	constants[num_constants++].value = value;
+}
+
+static const int get_constant(const char* name) {
+	for (int i = 0; i < num_constants; i++) { 
+		if (strcmp(constants[i].name, name) == 0) 
+			return constants[i].value;
+	}
+	return -1;
+}
+
 /****************************************************************************************/
 /* LABEL MANAGEMENT																		*/
 /****************************************************************************************/
@@ -167,7 +192,7 @@ static void register_label_address(const char* string) {
 			i++;
 		}
 	}
-	num_known_labels++;
+	//num_known_labels++;
 }
 
 static void generate_anonymous_labelname(char* dest) {
@@ -206,6 +231,14 @@ static void append_strings() {
 static void parse_expression();
 static void parse_statements();
 
+static void parse_strleft();
+static void parse_str();
+static void parse_chr();
+
+static void parse_strlen();
+static void parse_keypressed();
+static void parse_anykey();
+
 #define EXPECT(X, Y) if (tkn_get_token() != X) { parser_finished = true; error_raise(Y); return; }
 
 static void parse_concat_atom() {
@@ -227,6 +260,9 @@ static void parse_concat_atom() {
 		tkn_next();
 		return;
 	}
+	if (tkn_get_token() == TOKEN_STRLEFT) { tkn_next(); parse_strleft(); return; }
+	if (tkn_get_token() == TOKEN_STR) { tkn_next(); parse_str(); return;  }
+	if (tkn_get_token() == TOKEN_CHR) { tkn_next(); parse_chr(); return;  }
 	parser_finished = true; error_raise("Syntax error");
 	return;
 }
@@ -248,6 +284,13 @@ static void parse_expr_atom() {
 		return;
 	}
 	if (tkn_get_token() == TOKEN_IDENTIFIER) {
+		int constvalue = get_constant(tkn_get_string());
+		if (constvalue != -1) {
+			emmit(OP_PUSH);
+			emmit(constvalue);
+			tkn_next();
+			return;
+		}
 		int ivar = get_variable_index(tkn_get_string());
 		if (is_variable_array()) {
 			tkn_next(); EXPECT(TOKEN_LPAR, "Expected array index");
@@ -282,6 +325,10 @@ static void parse_expr_atom() {
 		tkn_next();
 		return;
 	}
+	if (tkn_get_token() == TOKEN_STRLEN) { tkn_next(); parse_strlen(); return; }
+	if (tkn_get_token() == TOKEN_KEYPRESSED) { tkn_next(); parse_keypressed(); return; }
+	if (tkn_get_token() == TOKEN_ANYKEY) { tkn_next(); parse_anykey(); return; }
+
 	parser_finished = true; error_raise("Syntax error");
 	return;
 }
@@ -339,6 +386,17 @@ static void parse_expression() {
 	}
 }
 
+static void parse_const() {
+	EXPECT(TOKEN_IDENTIFIER, "Expected identifier");
+	char constname[40];
+	strcpy(constname, tkn_get_string());
+	tkn_next(); EXPECT(TOKEN_EQ, "Expected '='");
+	tkn_next(); EXPECT(TOKEN_NUMBER, "Expected integer constant");
+	int constvalue = tkn_get_value();
+	parser_register_constant(constname, constvalue);
+	tkn_next();
+}
+
 static void parse_dim() {
 	EXPECT(TOKEN_IDENTIFIER, "Expected variable");
 	char varname[40];
@@ -674,9 +732,22 @@ static void parse_border() {
 	emmit_w(get_label_address("_sys_vdp_border"));
 }
 
+static void parse_clrscr() {
+	emmit(OP_JSR);
+	emmit_w(get_label_address("_sys_vdp_clrscr"));
+}
+
+static void parse_wait() {
+	parse_expression();
+	emmit(OP_SLEEP);
+}
+
+
 static void parse_statements() {
 	while (!parser_finished) {
 		switch (tkn_get_token()) {
+		case TOKEN_CONST:
+			tkn_next(); parse_const(); break;
 		case TOKEN_DIM:
 			tkn_next(); parse_dim(); break;
 		case TOKEN_LET:
@@ -704,16 +775,16 @@ static void parse_statements() {
 		case TOKEN_REM:
 			tkn_next(); break;
 
-		case TOKEN_STRLEFT:
-			tkn_next(); parse_strleft(); break;
-		case TOKEN_STRLEN:
-			tkn_next(); parse_strlen(); break;
+		//case TOKEN_STRLEFT:									<--- Parsed in parse_concat_atom
+		//	tkn_next(); parse_strleft(); break;
+		//case TOKEN_STRLEN:									<--- Parsed in parse_expr_atom
+		//	tkn_next(); parse_strlen(); break;
 		case TOKEN_DEBUG:
 			tkn_next(); parse_debug(); break;
-		case TOKEN_CHR:
-			tkn_next(); parse_chr(); break;
-		case TOKEN_STR:
-			tkn_next(); parse_str(); break;
+		//case TOKEN_CHR:
+		//	tkn_next(); parse_chr(); break;						<--- Parsed in parse_concat_atom
+		//case TOKEN_STR:
+		//	tkn_next(); parse_str(); break;						<--- Parsed in parse_concat_atom
 		case TOKEN_SETSPRITE:
 			tkn_next(); parse_setsprite(); break;
 		case TOKEN_PUTSPRITE:
@@ -726,16 +797,20 @@ static void parse_statements() {
 			tkn_next(); parse_putchar(); break;
 		case TOKEN_SETCHAR:
 			tkn_next(); parse_setchar(); break;
-		case TOKEN_KEYPRESSED:
-			tkn_next(); parse_keypressed(); break;
-		case TOKEN_ANYKEY:
-			tkn_next(); parse_anykey(); break;
+		//case TOKEN_KEYPRESSED:								<--- Parsed in parse_expr_atom
+		//	tkn_next(); parse_keypressed(); break;
+		//case TOKEN_ANYKEY:									<--- Parsed in parse_expr_atom
+		//	tkn_next(); parse_anykey(); break;
 		case TOKEN_UPDATESCR:
 			tkn_next(); parse_updatescr(); break;
 		case TOKEN_COLOR:
 			tkn_next(); parse_color(); break;
 		case TOKEN_BORDER:
 			tkn_next(); parse_border(); break;
+		case TOKEN_CLRSCR:
+			tkn_next(); parse_clrscr(); break;
+		case TOKEN_WAIT:
+			tkn_next(); parse_wait(); break;
 
 		case TOKEN_IDENTIFIER:
 			for (int i = 0; i < num_external_functions; i++) {
@@ -781,6 +856,10 @@ void parser_parse(const char* buffer, byte* mem) {
 	parse_statements();
 	append_strings();
 
+	FILE *f = fopen("test.bin", "wb");
+	fwrite(mem, codepos, 1, f);
+	fclose(f);
+
 	//return code;
 }
 
diff --git a/parser.h b/parser.h
index f43086b..c3b64bf 100644
--- a/parser.h
+++ b/parser.h
@@ -78,3 +78,4 @@ void parser_parse(const char* buffer, unsigned char* mem);
 const int parser_get_codesize();
 const int parser_get_memory_usage();
 void parser_register_external_function(const char* name, const int num_parameters);
+void parser_register_constant(const char* name, const unsigned char value);
\ No newline at end of file
diff --git a/rom.lbl b/rom.lbl
index 37a390c..5dbc3f5 100644
Binary files a/rom.lbl and b/rom.lbl differ
diff --git a/test.bas b/test.bas
index 422b424..6186cb2 100644
--- a/test.bas
+++ b/test.bas
@@ -1,21 +1,24 @@
-locate 2 1
-print "HOLA JAILERS"
-border 5
-spr = 250
-setsprite 0 spr 0
-x = 0
-dx = 1
-count = 5
+	border INK_BLACK
+	color INK_WHITE + PAPER_BLACK
+	clrscr
+	locate 4 2 print chr &h87, chr &h85, chr &h87, chr &h85, chr &h87, chr &h85, chr &h87, chr &h81
+	locate 4 3 print chr &h85, chr &h85, chr &h85, chr &h85, chr &h85, chr &h85, chr &h85, chr &h84
+	locate 4 4 print chr &h87, chr &h81, chr &h8D, chr &h85, chr &h85, chr &h85, chr &h8D, chr &h85
+	locate 3 8 print "PRESS SPACE"
+	updatescr
+	x = 0
+	dx = 1
+	setsprite 0 &HF9 INK_RED
 peiv:
-putsprite 0 x 60
-updatescr
-x = x + dx
-if x = 128 then dx = -1 end
-if x = 8 then dx = 1 end
-dec count
-if count = 0 then
-	count = 5
-	if spr = 250 then spr = 251 else spr = 250 end
-	setsprite 0 spr 1
-end
-goto peiv
\ No newline at end of file
+	putsprite 0 x 40
+	putsprite 0 x 40
+	putsprite 0 x 40
+	updatescr
+	if anykey then goto continuar end
+	goto peiv
+continuar:
+	clrscr
+	locate 0 0 print "Ok"
+	updatescr
+ttt:
+	goto ttt
\ No newline at end of file
diff --git a/tokenizer.cpp b/tokenizer.cpp
index ba40913..8c641ad 100644
--- a/tokenizer.cpp
+++ b/tokenizer.cpp
@@ -1,4 +1,5 @@
 #include "tokenizer.h"
+#include "error.h"
 
 static bool streq(const char* a, const char* b) {
 	while (*a != 0 && *b != 0) {
@@ -42,6 +43,7 @@ t_token_op tkn_tokens[] = {
 	{ "not", TOKEN_NOT },
 	{ "mod", TOKEN_MOD },
 	{ "dim", TOKEN_DIM },
+	{ "const", TOKEN_CONST },
 	{ "inc", TOKEN_INC },
 	{ "dec", TOKEN_DEC },
 	{ "strleft", TOKEN_STRLEFT },
@@ -60,8 +62,12 @@ t_token_op tkn_tokens[] = {
 	{ "updatescr", TOKEN_UPDATESCR },
 	{ "color", TOKEN_COLOR },
 	{ "border", TOKEN_BORDER },
+	{ "clrscr", TOKEN_CLRSCR },
+	{ "wait", TOKEN_WAIT },
 };
 
+static char hex_digit(const char digit) { return digit - (digit < 57 ? 48 : 55); }
+
 #define CCHR *ptr
 #define NEXT if(*ptr==10){line++;row=0;}else{row++;};ptr++
 
@@ -80,7 +86,7 @@ static void tkn_do_next() {
 	if (CCHR == 34) {
 		NEXT;
 		while (CCHR != 0 && CCHR != 34) { *id = CCHR; id++; NEXT; }
-		if (CCHR == 0) { current_token = TOKEN_ERROR; return; }
+		if (CCHR == 0) { current_token = TOKEN_ERROR; error_raise("Unexpected end of file."); return; }
 		*id = 0; NEXT;
 		current_token = TOKEN_STRING; return;
 	}
@@ -122,6 +128,27 @@ static void tkn_do_next() {
 	if (CCHR == '%') { NEXT; current_token = TOKEN_MOD; return; }
 	if (CCHR == 39)  { NEXT; current_token = TOKEN_REM; while (CCHR != 0 && CCHR != 10) { NEXT; };  return; }
 
+	if (CCHR == '&') {
+		NEXT;
+		if ((CCHR | 32) == 'h') {
+			NEXT;
+			if ((CCHR >= 48 && CCHR <= 57) || (CCHR >= 65 && CCHR <= 70)) {
+				do { value = (value << 4) + hex_digit(CCHR); NEXT; } while ((CCHR >= 48 && CCHR <= 57) || (CCHR >= 65 && CCHR <= 70));
+				current_token = TOKEN_NUMBER; return;
+			}
+		}
+		if ((CCHR | 32) == 'b') {
+			NEXT;
+			if (CCHR == 48 || CCHR == 49) {
+				do { value = (value << 1) + (CCHR-48); NEXT; } while (CCHR == 48 || CCHR == 49);
+				current_token = TOKEN_NUMBER; return;
+			}
+		}
+		current_token = TOKEN_ERROR;
+		error_raise("Syntax error");
+		return;
+	}
+
 	// if no match, it's an error
 	current_token = TOKEN_ERROR; return;
 }
diff --git a/tokenizer.h b/tokenizer.h
index 54f6bc2..9904db8 100644
--- a/tokenizer.h
+++ b/tokenizer.h
@@ -11,6 +11,7 @@ enum t_tokentype {
 	TOKEN_IDENTIFIER,
 	TOKEN_LABEL,
 	TOKEN_DIM,
+	TOKEN_CONST,
 
 	TOKEN_LET,
 	TOKEN_IF,
@@ -66,6 +67,8 @@ enum t_tokentype {
 	TOKEN_UPDATESCR,
 	TOKEN_COLOR,
 	TOKEN_BORDER,
+	TOKEN_CLRSCR,
+	TOKEN_WAIT,
 };
 
 void tkn_init(const char* buffer);
diff --git a/vbvm.vcxproj b/vbvm.vcxproj
index e3faf46..70777dc 100644
--- a/vbvm.vcxproj
+++ b/vbvm.vcxproj
@@ -88,6 +88,7 @@
     <ClCompile Include="vm.cpp" />
   </ItemGroup>
   <ItemGroup>
+    <ClInclude Include="constants.h" />
     <ClInclude Include="error.h" />
     <ClInclude Include="font.h" />
     <ClInclude Include="parser.h" />
diff --git a/vbvm.vcxproj.filters b/vbvm.vcxproj.filters
index c28762b..1c443c9 100644
--- a/vbvm.vcxproj.filters
+++ b/vbvm.vcxproj.filters
@@ -62,5 +62,8 @@
     <ClInclude Include="parser.h">
       <Filter>Header Files</Filter>
     </ClInclude>
+    <ClInclude Include="constants.h">
+      <Filter>Header Files</Filter>
+    </ClInclude>
   </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/vdp.cpp b/vdp.cpp
index 42f6c81..39beb3d 100644
--- a/vdp.cpp
+++ b/vdp.cpp
@@ -13,6 +13,7 @@
 #define VDP_CMD_FLIP		6
 #define VDP_CMD_COLOR		7
 #define VDP_CMD_BORDER		8
+#define VDP_CMD_CLRSCR		9
 
 struct t_sprite {
 	Uint8 x = 0;
@@ -96,7 +97,7 @@ void vdp_quit() {
 	SDL_Quit();
 }
 
-static void flip() {
+void vdp_flip() {
 	Uint8* sb = screen_buffer;
 	Uint8* sm = screen_map;
 	Uint8* sc = screen_color;
@@ -191,7 +192,7 @@ void vdp_cmd_out(const unsigned char& value) {
 		sprites[n].col = data_stack[data_stack_pos - 3] & 0xF;
 		break;
 	case VDP_CMD_FLIP:
-		flip(); break;
+		vdp_flip(); break;
 	case VDP_CMD_COLOR:
 		color = data_stack[0];
 		break;
@@ -199,6 +200,10 @@ void vdp_cmd_out(const unsigned char& value) {
 		border = data_stack[0] & 0xF;
 		SDL_SetRenderDrawColor(sdlRenderer, palette[border][0], palette[border][1], palette[border][2], palette[border][3]);
 		break;
+	case VDP_CMD_CLRSCR:
+		for (int i = 0; i < 16 * 12; i++) screen_map[i] = 32;
+		for (int i = 0; i < 16 * 12; i++) screen_color[i] = color;
+		break;
 	}
 	data_stack_pos = 0;
 }
diff --git a/vdp.h b/vdp.h
index 2d5ac40..1344a00 100644
--- a/vdp.h
+++ b/vdp.h
@@ -2,7 +2,7 @@
 
 void vdp_init();
 void vdp_quit();
-
+void vdp_flip();
 void vdp_data_out(const unsigned char& value);
 void vdp_cmd_out(const unsigned char& value);
 unsigned char vdp_in();
diff --git a/vm.cpp b/vm.cpp
index 726b9ec..5e2f633 100644
--- a/vm.cpp
+++ b/vm.cpp
@@ -3,6 +3,8 @@
 #include <stdlib.h>
 #include "parser.h"
 #include "error.h"
+#include "constants.h"
+#include <SDL.h> // For SDL_Delay
 
 #define MAX_EXTERNAL_CALLS	256
 #define MAX_DATA_STACK		256
@@ -116,30 +118,22 @@ static void load_rom() {
 }
 
 static void load_program(const char* filename) {
-/*	FILE *f = fopen(filename, "rb");
-	fseek(f, 0, SEEK_END);
-	long fsize = ftell(f);
-	fseek(f, 0, SEEK_SET);
-	fread(mem, fsize, 1, f);
-	fclose(f);*/
 	FILE *f = fopen(filename, "rb");
 	fseek(f, 0, SEEK_END);
 	long fsize = ftell(f);
 	fseek(f, 0, SEEK_SET);  //same as rewind(f);
-
 	char *program = (char*)malloc(fsize + 1);
 	fread(program, fsize, 1, f);
 	fclose(f);
-
 	program[fsize] = 0;
 
-	//unsigned char* rawCode =
+	register_constants();
+
 	parser_parse(program, mem);
 	free(program);
 
 	if (error_raised()) {
 		error_print();
-		//getchar();
 	}
 	else {
 		printf("Compilation complete!\nProgram size: %d bytes\nMemory usage: %d bytes\n", parser_get_codesize(), parser_get_memory_usage());
@@ -240,7 +234,7 @@ const int vm_step() {
 	case OP_GEQ: stack_push(vm_datastack, stack_pop(vm_datastack) >= stack_pop(vm_datastack)); vm_cycles++; break;
 	case OP_IN: stack_push(vm_datastack, in_ports[vm_program[vm_pc++]]()); vm_cycles++; break;
 	case OP_OUT: out_ports[vm_program[vm_pc++]](stack_pop(vm_datastack)); vm_cycles++; break;
-	case OP_SLEEP: sleeping = true; vm_cycles++; break;
+	case OP_SLEEP: SDL_Delay(stack_pop(vm_datastack) * 1000); vm_cycles++; break;
 	}
 	return vm_cycles;
 }